He hit a ball down toward the right field corner and looked like he may attempt to leg out a double but then slowed up coming around first and looked like his leg (I thought his left) grabbed him a bit. He looked like he was clearly frustrated throwing his batting gloves down on the ground.
Edit to add, even if he didn't pull a muscle, he likely was only going to stay at 1B on that hit as Reynolds got to the ball quickly. So it wasn't the muscle pull - or whatever it was - that led to him staying at 1B.