Here's slo-mo footage of the Yankees catcher's home-run yesterday at whatever field the Kansas City Royals "play" on.
Here's a link to additional HD MLB.com evidence. Best I can tell, the ball had entered slightly to the right of the spine. It traveled downward and exited from the front of the neck, causing a nick in the Royals' fan V-neck T-shirt. It was a cruel and shocking act of violence directed against a man, a family, a nation, and against all mankind.
Oh, apparently one of Posada's teammates hit a few more round-trippers, too. But whatever. That still doesn't explain why the other douchebag in centerfield flopped.