Correa, Appel headline Astros' updated Top 20 list

Six Houston prospects also make overall Top 100 Prospects at midseason revamp

Correa, Appel headline Astros' updated Top 20 list

With the passing of the Draft signing deadline, teams have had a recent influx of talent into their farm systems, and with that, we've updated the Top 20 Prospects lists of all 30 teams.

To be on a list, a player must have rookie eligibility. To qualify for rookie status, a player must not have exceeded 130 at-bats or 50 innings pitched in the Major Leagues, or accumulated more than 45 days on the active roster of a Major League club or clubs during the 25-player limit period, excluding time on the disabled list or in military service.

Players are graded on a 20-80 scale for future tools -- 20-30 is well below average, 40 is below average, 50 is average, 60 is above average and 70-80 is well above average.

Check out all 30 team Top 20 lists and the Top 100 on Prospect Watch.

1. Carlos Correa, SS
Preseason rank: 1
MLB Top 100 rank: 3 (Preseason: 8)
ETA: 2016
Scouting grades: Hit: 60 | Power: 70 | Run: 50 | Arm: 70 | Field: 50 | Overall: 70

In a Draft class that also included Byron Buxton and Mark Appel, Correa was something of a surprise as the No. 1 overall pick by the Astros in 2012. But Correa was worthy of the selection, and he showed why in 2013, his first full professional season. As an 18-year-old, Correa helped lead Class A Quad Cities to the Midwest League title, and he led the circuit with a .872 OPS. He was on his way to a similar performance in 2014 when a broken right fibula ended his season.

Though Correa is still physically maturing, he already has above-average power. Correa has a balanced swing and he has a good approach at the plate. He is an average runner. Correa has a strong arm, soft hands and good defensive instincts, all of which could help him stay at shortstop. Some scouts feel he will outgrow the position, but so far, he has shown he can handle shortstop. 

Correa earns high marks for his work ethic and makeup, which will help him bounce back from his injury. He has a chance to be an impact player regardless of his future position.

2. Mark Appel, RHP
Preseason rank: 2
MLB Top 100 rank: 46 (Preseason: 17)
ETA: 2015
Scouting grades: Fastball: 70 | Slider: 65 | Changeup: 55 | Control: 55 | Overall: 60

Appel was considered by many to be one of the top prospects in the 2012 Draft, but he fell to the Pirates at No. 8 for a variety of reasons. He eventually chose not to sign, and instead he returned to Stanford for his senior season. Appel was once again considered among the top prospects in 2013, and the Astros didn't pass on him a second time, selecting the Houston native first overall.

After Appel's solid showing in his professional debut last summer, he got a late start to the 2014 season due to an appendectomy in January. He never seemed to be able to get back on track at Class A Advanced Lancaster. 

Appel's struggles are difficult to explain, because his stuff hasn't taken a step back from what he showed at Stanford. He throws his fastball in the mid-to-upper 90s, mixing it with a changeup and a slider. Appel throws all of his pitches for strikes and he has ideal size for a right-hander.

3. Domingo Santana, OF
Preseason rank: 8
MLB Top 100 rank: 56 (Preseason: NA)
ETA: 2014
Scouting grades: Hit: 45| Power: 60 | Run: 50 | Arm: 60 | Field: 50 | Overall: 55

Originally signed by the Phillies in 2009, Santana was acquired as the player to be named later to complete the package of prospects Philadelphia sent to the Astros in exchange for Hunter Pence at the Trade Deadline in '11.

Since debuting as a 16-year-old in the Gulf Coast League, Santana has always been young for his league. That hasn't stopped him from producing solid offensive numbers at each stop in his Minor League career. There is a lot of swing-and-miss in Santana's game, and he struck out at least 130 times in each of his first three years in full-season ball. That doesn't prevent him from using his big raw power to drive the ball out to every area of the field.

Santana is an average defender and has a strong arm. Big and physical, he fits the prototypical profile for a power-hitting right fielder.

4. Mike Foltynewicz, RHP
Preseason rank: 6
MLB Top 100 rank: 65 (Preseason: 54)
ETA: 2014
Scouting grades: Fastball: 80 | Curveball: 50 | Changeup: 50 | Control: 45 | Overall: 55

Since his breakout season in 2012, Foltynewicz has continued to make rapid progress toward the Major Leagues.

Foltynewicz is a pure power pitcher. His fastball sits in the mid-to-upper 90s, and it has been clocked in the triple digits. Like most young flamethrowers, Foltynewicz is still working tighten up his command and improve the consistency of his offspeed pitches. His changeup is his best secondary offering, and his downer curveball has the promise of giving him another average or better pitch.

As the club does with most of its pitching prospects, Houston has used Foltynewicz as both a starter and a reliever. While some scouts see him as a closer, Foltynewicz has the tools necessary to fit into a Major League rotation one day.

5. Lance McCullers, RHP
Preseason rank: 5
MLB Top 100 rank: 83 (Preseason: 52)
ETA: 2016
Scouting grades: Fastball: 70 | Curveball: 65 | Changeup: 45 | Control: 45 | Overall: 55 

McCullers was considered one of the top high school pitchers in the 2012 Draft, but he slid due to signability. The Astros were able to ink him, and he made an impressive full-season debut at Class A Quad Cities in 2013.

McCullers, the son of the former Padres right-hander by the same name, succeeds thanks to his excellent fastball-curveball combination. His fastball sits in the mid-to-upper 90s, with good movement. McCullers' breaking ball has different shapes and sizes, but the best ones look like hard late curveballs.

The rest of McCullers' game isn't as advanced as those two pitches, but it shows promise. Though he has improved his changeup as a professional, he still has work to do on the pitch and he needs to tighten his command. Some scouts still feel McCullers is best suited for a role in short relief like his father, but there is growing sentiment that he can make it as a starter.

6. Michael Feliz, RHP
Preseason rank: 10
MLB Top 100 rank: 99 (Preseason: NA)
ETA: 2017
Scouting grades: Fastball: 65 | Slider: 55 | Changeup: 50 | Control: 50 | Overall: 55 

Originally signed by the A's as a 16-year-old in 2010, Feliz's contract was voided when he tested positive for steroids. The Dominican native ultimately landed with the Astros, and after sitting out a 50-game suspension, he showed his vast potential on the mound.

Feliz's fastball sits comfortably in the mid-90s, and it has touched 98 mph. His slider flashes plus potential, and his changeup gives him a third quality offering. Feliz throws a lot of strikes, but he may need to refine his delivery to truly command all of his pitches.

Though Feliz is still raw, he demonstrates a good feel for pitching. He won the New York-Penn League ERA title as a 19-year-old in 2013, and he earned a spot on the World roster at the 2014 SiriusXM All-Star Futures Game the following year.

7. Vincent Velasquez, RHP
Preseason rank: 9
ETA: 2016
Scouting grades: Fastball: 60 | Curveball: 50 | Changeup: 60 | Control: 50 | Overall: 55 

The 58th overall pick in the 2010 Draft, Velasquez has rebounded well since undergoing Tommy John surgery and missing the '11 season. In 2013, he threw more than 100 innings for the first time in his career and he reached the California League.

Velasquez throws his fastball in the low-90s, and he regularly reaches back for a bit more velocity. Despite his relative inexperience, he has a plus changeup. Velasquez's curveball needs more refinement, but it should give him another quality offering in time. He earns praise for his makeup and his confident demeanor on the mound.

Velasquez started the season strong before a groin injury sidelined him for two months. When he's healthy, he fits right in with the rest of the Astros' top pitching prospects.

8. Rio Ruiz, 3B
Preseason rank: 11
ETA: 2016
Scouting grades: Hit: 55 | Power: 55 | Run: 30 | Arm: 55 | Field: 50 | Overall: 50 

A top high school prospect in the 2012 Draft class, Ruiz slid after a blood clot in his shoulder sidelined him for part of the season. Houston used its financial flexibility to sign him, and the organization teamed him with Correa.

After Ruiz struggled at the outset of his first full professional season, he made a mechanical adjustment in his swing and he finished the season strong. Ruiz has a good approach at the plate, and his sweet swing generates a lot of bat speed -- giving him above-average power. He is a below-average runner and doesn't have great range at third base. Still, Ruiz has the potential to be an average defender.

The Astros were encouraged by how well Ruiz made the adjustment to his swing in 2013. His success this season in the California League has only reinforced their confidence in him.

9. Josh Hader, LHP
Preseason rank: 15
ETA: 2016
Scouting grades: Fastball: 60 | Slider: 45 | Changeup: 50 | Control: 45 | Overall: 50 

Hader was lightly scouted as a lankly and soft-tossing left-hander, but the Orioles took a flier on the local high school product in the 19th round. Since then, Hader has made significant strides, and he was one of the key pieces Houston acquired in exchange for Bud Norris at the 2013 Trade Deadline.

Hader's velocity has improved significantly since he signed. His fastball now sits around 90 mph, and it has reached as high as 96 mph. While Hader's already gotten stronger since signing, there's even more projection left in his frame. His body type and his low three-quarters arm slot lead to comparisons to Chris Sale.

Even with all of his advances so far, Hader still has plenty of room for growth. His secondary pitches have good potential, but they are inconsistent. Hader needs to refine his command. He started making those adjustments in 2014 at Class A Lancaster, where he has thrived despite pitching in one of the most hitter friendly parks in the Minor Leagues.

10. Teoscar Hernandez, OF
Preseason rank: 13
ETA: 2016
Scouting grades: Hit: 50 | Power: 50 | Run: 60 | Arm: 55 | Field: 50 | Overall: 50

Hernandez was unheralded as an amateur in the Dominican Republic, signing for just $20,000 in 2011. Three years later, it looks like the Astros got quite the bargain.

Hernandez is a potential five-tool player with no real weaknesses. He generates excellent bat speed with a quick and aggressive swing. There's some swing-and-miss in Hernandez's game, but he makes enough contact to be a quality all-around hitter.

Hernandez has a strong arm and is a capable center fielder. He is still physically maturing, though, and if he loses a bit of speed as he fills out, he'll likely need to move to a corner. Even if a position change does come to pass, Hernandez has the tools to be an everyday player.

11. Delino DeShields, OF
Preseason rank: 7
MLB Top 100 rank: NA (Preseason: 66)
ETA: 2015
Scouting grades: Hit: 50 | Power: 45 | Run: 70 | Arm: 50 | Field: 55 | Overall: 50 

Much like his father, a former Major League outfielder by the same name, DeShields profiles as a leadoff hitter. He is an above-average runner who knows how to use his speed on the basepaths. DeShields stole 101 bases in 2012, and while that total fell to 51 in '13, he remains a threat to run anytime he gets on base. 

DeShields has a quick and compact swing, and he does a good job of putting the bat on the ball. His quick wrists generate good bat speed and a surprising amount of pop. 

Houston made DeShields a second baseman after drafting him in the first round in 2010, but then moved him back to his natural position of center field during the Arizona Fall League in '13. He is a good fit in the outfield, where his speed plays up.

12. Derek Fisher, OF
Preseason rank: None (CBA)
ETA: 2017
Scouting grades: Hit: 55 | Power: 55 | Run: 60 | Arm: 40 | Field: 45 | Overall: 50

Fisher was one of the top high school hitting prospects in the 2011 Draft, but he decided to attend Virginia instead of signing. A strong showing in the Cape Cod League last summer helped push him up Draft boards again in 2014, despite missing six weeks of his junior season due to a broken hamate bone.

Fisher's tools grade out well, though that didn't always lead to consistent production in college. Fisher has a smooth left-handed swing, and he projects as a plus hitter in terms of both average and power. Basestealing isn't a big part of Virginia's offensive philosophy, but he has the speed necessary to make noise on the basepaths as a professional.

Though Fisher has good speed, his below-average arm limits him to left field. Although that puts more pressure on his bat, his tools give him the chance to be an impact hitter.

13. Nick Tropeano, RHP
Preseason rank: 17
ETA: 2014
Scouting grades: Fastball: 60 | Slider: 45 | Changeup: 55 | Control: 50 | Overall: 50 

Tropeano has made significant strides since being drafted out of Stony Brook in 2011. He learned to rely more on his fastball and pitch down in the zone more effectively. Tropeano led all Astros Minor Leaguers in strikeouts in 2012, and he has put himself on the cusp of the Major Leagues with a strong showing this season at Triple-A Oklahoma City.

Tropeano's low-90s fastball and changeup give him two above-average offerings. His slider has a tendency to get slurvy, and it needs further refinement. Tropeano has solid control, and he earns praise for his aggressive demeanor on the mound.

Tropeano's slider is the key to his development. If he can tighten it up and give himself a third quality offering, he will fit nicely into a Major League rotation.

14. A.J. Reed, 1B
Preseason rank: None (2014 Draft)
ETA: 2017
Scouting grades: Hit: 55 | Power: 60 | Run: 30 | Arm: 60 | Field: 50 | Overall: 50

The Mets took Reed as a left-handed pitcher in the 25th round of the 2011 Draft. Instead of signing, he went on to become the ace at the University of Kentucky. Reed's pitching days are behind him, however, after he led the country with 23 home runs this spring. His two-way play helped him win the 2014 Golden Spikes Award as the best amateur player in the country.

Reed has the kind of left-handed power that is difficult to find, and he's more than just a masher. He has made significant strides as a hitter. Reed is making more consistent hard contact without sacrificing any pop.

Reed doesn't run well enough to play a position other than first base, but he has a strong arm and he plays solid defense. Scouts believe he has the tools to become a power-hitting first baseman in the big leagues.

15. Kyle Smith, RHP
Preseason rank: 19
ETA: 2015
Scouting grades: Fastball: 50 | Curveball: 60 | Changeup: 50 | Control: 55 | Overall: 45

Smith's advanced pitchability helped him hit the ground running as a professional, and he quickly mastered the low Minors. It also attracted the attention of Houston, which acquired him from the Royals in exchange for Justin Maxwell at the 2013 Trade Deadline.

Smith throws his fastball around 90 mph, and he makes up for its average velocity with solid control. His best pitch is his tight downer curveball, and he has a good feel for his changeup.

Smith mixes all of his pitches well and doesn't back down from hitters, despite his lack of power stuff. His ceiling doesn't match that of some of the Astros' top pitching prospects, but he has all the tools necessary to one day help Houston's rotation.

16. Nolan Fontana, 2B/SS
Preseason rank: 18
ETA: 2015
Scouting grades: Hit: 45 | Power: 30 | Run: 50 | Arm: 50 | Field: 50 | Overall: 45 

Even at Florida, where he was the starting shortstop for a team that reached the College World Series three years in a row, Fontana's tools have never stood out. Yet he seems to always find a way to get the job done and get the most out of his ability.

Fontana has a good approach at the plate and he has exceptional plate discipline. He has below-average power and sprays line drives to all areas of the field. Fontana is a solid defender at shortstop with a good arm. He's a heady player, which helps all of his tools play up.

Fontana may profile more as a utilityman than an everyday player, but scouts don't doubt that he'll find a way to make an impact in the Major Leagues. His progress has been slowed this season when he broke a finger in June. The injury required surgery, and it will keep Fontana out for several weeks.

17. Tony Kemp, 2B
Preseason rank: None
ETA: 2015
Scouting grades: Hit: 50 | Power: 30 | Run: 60 | Arm: 50 | Field: 45 | Overall: 45 

Kemp had an illustrious career at Vanderbilt, earning Southeastern Conference Freshman of the Year honors in 2011 and SEC Player of the Year honors in '13 -- making him the third player in conference history to win both awards. Despite his success, questions remained about Kemp's upside as a professional because of his size.

Kemp's game is well-suited for the top of the order. He combines his good on-base skills with above-average speed, and he has an understanding of how to use it on the bases. Kemp has made strides defensively, though he is still somewhat raw after spending much of his college career as an outfielder.

As an undersized and speedy second baseman, comparisons to Jose Altuve are inevitable for Kemp. He still has a ways to go to match Altuve's success, but he is off to a good start. Kemp reached Double-A Corpus Christi in his first full professional season.

18. Max Stassi, C
Preseason rank: 12
ETA: 2014
Scouting grades: Hit: 40 | Power: 55 | Run: 30 | Arm: 55 | Field: 50 | Overall: 45

Originally drafted by the A's, Stassi was part of the package dealt to Houston in February 2013 in exchange for Jed Lowrie and Fernando Rodriguez. Stassi broke out in his first year in the Astros' system, and he made his Major League debut last August.

Stassi has a simple swing and is at his best using an up-the-middle approach. He has solid power, and he has tapped into it more as the quality of his at-bats have improved. Stassi is solid defensively, and he earns praise for his handling of pitchers.

Injuries have dogged Stassi throughout his career, even forcing him onto the disabled list during his brief stint in the big leagues. If he can stay healthy, Stassi has the potential to contribute on a more regular basis soon in the Major Leagues.

19. Preston Tucker, OF
Preseason rank: None
ETA: 2015
Scouting grades: Hit: 45 | Power: 55 | Run: 30 | Arm: 40 | Field: 45 | Overall: 45

Tucker anchored the University of Florida's offense for four years, helping the Gators reach the College World Series three consecutive times. He has continued to hit as a professional, impressing Astros general manager Jeff Luhnow, who said he hopes Tucker can develop into "the Allen Craig" of Houston's system.

Tucker has flown a little under the radar despite his long track record. He has a good feel for hitting and he doesn't strike out much. Tucker's power is his best tool, and his 25 home runs in 2013 ranked second among all Astros Minor Leaguers.

Tucker has moved between first base and the outfield corners throughout his career. He has the ability to be a serviceable outfielder, but it will be up to his bat to carry him to the Major Leagues

20. Danry Vasquez, OF
Preseason rank: 20
ETA: 2016
Scouting grades: Hit: 55 | Power: 45 | Run: 40 | Arm: 40 | Field: 40 | Overall: 45

Originally signed by the Tigers out of Venezuela in 2010, Vasquez was dealt to Houston for Jose Veras at the '13 Trade Deadline. He has developed a solid reputation as a hitter, and he has produced good batting averages and low strikeout totals throughout his young career.

Vasquez has a quick and balanced swing, and he has a good feel for the barrel, which helps him hit line drives to all areas of the field. So far, that hasn't translated into much power, but scouts expect that he will develop power as he physically matures.

Vasquez is a below-average runner, limiting him defensively. He is passable in left field, but his bat will have to continue to produce as he advances through the Minor Leagues.

Teddy Cahill is a reporter for MLB.com. Follow him on Twitter at @tedcahill. This story was not subject to the approval of Major League Baseball or its clubs.