Brandon McCarthy left in the fourth inning against the Los Angeles Angels on Wednesday after a hard line drive off the bat of Erick Aybar hit Oakland's opening-day starter in the head.
McCarthy was taken to Alta Bates Summit Medical Center in Oakland as a precaution. The team said he never lost consciousness.
McCarthy had almost no time to react when Aybar lined his 91 mph cutter back. The ball bounced off the right side of McCarthy's head, knocking the A's pitcher down. He also landed on his head on the infield grass.
Third baseman Josh Donaldson picked up the deflected ball and threw out Morales for the second out of the inning.
McCarthy curled up in a ball and was writhing in pain. Team trainers checked on McCarthy for several minutes as A's players huddled around the infield and on the top step of the dugout.
Aybar stood on first base and looked on with concern. He could be seen in the Angels' dugout later sitting with his head down and his hands over his head.
McCarthy eventually sat up and ran his hands through his hair and around his head. He walked off the mound under his own power to an ovation from the Oakland Coliseum crowd.
McCarthy left with Oakland trailing 3-1. He allowed five hits, struck out three and walked one intentionally. Travis Blackley entered in relief.
McCarthy began the day with an 8-5 record and a 3.10 ERA.