Tampa Bay Rays right-hander Alex Cobb was taken off the field on a stretcher after it appeared he was hit near the right ear by a liner off the bat of Kansas City's Eric Hosmer in the fifth inning of Saturday's game.
Cobb put a hand on his head after being struck. Trainers from both teams and other medical staff immediately ran onto the field.
Cobb could be seen kicking his legs while being examined on the mound.
Players on both teams had hands on their hands as a stunned silence overtook Tropicana Field after the crowd gasped when Cobb was struck.
It came a month after Blue Jays starter J.A. Happ was also struck by a liner against the Rays and suffered a skull fracture.