Pirates shortstop Clint Barmes squared up to bunt with a runner at first base and no outs in the eighth and pulled his bat back just as the ball glanced off the bat and rolled foul. He was originally called out, before the umpires huddled and determined Barmes wasn't trying to bunt when the ball hit his bat. He wound up grounding out.
Mills came out of the dugout and argued at length with first base umpire and crew chief Jim Joyce before getting tossed.
"I was contending that he was still bunting, and the umpires felt no, he pulled it back and he wasn't bunting," said Mills, who was ejected five times last year. "Obviously, we had a disagreement. And that was it."
After the game, Astros closer Brett Myers presented Mills was the game ball for standing up for the team.