To the ones arguing that Kelce was justified in retaliating....the problem is where do you draw the line?
This works both ways. For those saying that Kelce should have just sat there and taken it, where do you draw the line? What if this kid followed Kelce around for the entire day? What if he intentionally bought tickets in the seat next to him just so he could taunting him throughout the game? What if, instead of calling Kelce's brother a "faggot," he mocked his wife for having a miscarriage?
(I don't know if Jason Kelce is married or even seeing somebody -- just making a hypothetical that would put most people in face-punching territory).
I am fine with a line that says "Shove a phone in somebody's face with fighting words attached, and you can reasonably expect to get your phone broken." That seems like good middle ground to me.