First let me start with saying that I never want anyone to get injured.

Did you see on that long TD run, how he slowed down around the 20 or so and then looked back around the 10 and had to suddenly increase his speed to avoid getting tackled? I think that sudden jolt of speed is probably where he tweaked his hamstring. It was a surprise to him and and unexpected pull on this leg to increase speed like that. Just my opinion.