A friend of mine attended the Eagles-Texans games in 2002 with Texans gear on. He said it was a little scary.
Honestly, pro football fans just don't have enough passion to get into too much violence. I attended an Oilers game (Falcons during the Oilers' big winning streak) in 1993 and sat on the first level. There were two women in front of me who never even looked at the field - they just chattted with each other the whole game.
In my section, the turnover of attendees from week to week is very high. Meanwhile, I leave every game without my voice. There's basically one loud fan in every section (I'm the one in mine). Everyone else is hanging out at the concesssion stand and telling each other ridiculous sports legends like that Texans were allowed one draft pick in 2001 and passed up Michael Vick. RME.
I'm not bitter or anything.