Jason Kelce lost it at a person in Pennsylvania ... grabbing someone's phone and throwing it to the ground before storming off -- right after someone in the crowd called Travis a gay slur.
The former NFL star-turned-commentator was in Happy Valley for the matchup between Ohio State and Penn State Saturday morning, and a crowd started following the star ... cheering him on and asking for fist bumps at first.
It didn't stay positive for long though .