Looks like JT Snow hurt his foot while trying to catch a foul ball. His foot caught on the edge of the grass and warning track near the tarp. It's been raining there, so the wet ground may have something to do with it. Doesn't look serious, but he came out of the game.

Correction: As pointed out in the comments, it was Lance Niekro, not Snow. Snow would have made the play, which should have been my first clue.