Posey actually remained in the game to finish that inning, but he was lifted for a pinch-hitter in the next half-inning. The Giants say he is heading for further evaluation.
Any time you see a headshot like that, the concern has to be a concussion. Countless catchers have been concussed on similar plays, including Joe Mauer just last season. He was sidelined for six weeks.
Posey, 27, came into Sunday's game hitting .269/.329/.420 (115 OPS+) with nine home runs in 61 games. The Giants have a comfortable 6.5-game lead in the NL West, but losing their starting backstop for any length of time would be devastating.