...it looked like BYU was playing zone, he passed off the player to another DB - and the other DB slipped and fell down. So at that point the guy who passed him off started running towards him - but cut off short as he knew there was no way he would catch up.

At least that's what it looked like to me. There was a DB with the WR momentarily, who slipped and fell down. And that's when Tanner - the guy the commentators were talking about - started running towards him too late.

I'm not sure what his assignment was, of course, or if he was supposed to stay with the guy so he had over/under coverage versus just passing him off. I'm just stating what I saw and my interpretation.