I agree 100%. The kids were clearly not 100 percent right. Many (if not all) of them had no right to be there, and they deserved to have the police called on them to come and boot them from the area.
But, at the same time, that does not mean that the officer was justified in behaving as he did. The other 11 officers at the scene handled the situation very well, but the officer who resigned did not.
Assuming the lawyer’s statement about the two suicide calls is accurate (and I have no reason to think it’s not), I sympathize with the officer. Two emotionally-draining calls, and then he’s thrust into a difficult, tense crowd situation? That’s a tough, tough day for any officer. But part of the (extremely difficult) job of being a police officer is maintaining composure—even in very difficult situations, and even on very tough days. He did not do that. I hope this is a learning experience for him.
What, you mean the guys who showed up later? After he had to deal with all that rabble by himself? Yeah, it's a lot easier to retain composure when you are not the only guardian of civilization on the field.