Cosart was traded along with infielder Enrique Hernandez and Minor League outfielder Austin Wates.
"It hurts a lot just based on the fact he's a hometown boy and also, he had a chance to do special things here," pitcher Dallas Keuchel said. "He's only 24 years old and showed a lot of promise. I was kind of shocked by it, but it's a business, and everybody is trying to get better. We'll see."
Cosart was close with several of his teammates. He served as best man in Josh Zeid's wedding -- they came to Houston together in a trade with Philadelphia -- and was rooming with Collin McHugh and is best friends with Brad Peacock, who was recently sent to Triple-A.
The trade took Jose Altuve by surprise.
"Kike just got here, and all he did was hit," Altuve said. "That's why he got traded. Cosie, I think he's been one of my best friends here on the team. I feel sad, but at the same time, I'm happy, because I know it's going to be good for them, and I know they're going to have a good career with the Miami Marlins."
Veteran catcher Jason Castro took it all in stride. He's seen numerous trades in his time with the Astros, and every player who was in the lineup with him when he made his Major League debut in 2010 has since been dealt.
"All we can do, what we can concern ourselves with, is preparing to win," Castro said. "When the time is right, we'll be consistent, and we'll put the best team possible on the field. That's really all we're concerned with as players -- playing our game and doing what we can every day to get better."
Brian McTaggart is reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.