I'm a huge football fan, and have gone to 8+ games a year for the last 10 years of my life. I played 12 years of hockey when I was younger. I have a pretty good understanding of sportsmanship.
I can tell you for a fact, you would be escorted out by security if you start calling people %%%gots. Booing is one thing, person attacks are yet another. Certain things are accepted in society, and certain things are not. Just like certain things in League are tolerated. The last Rams home game, I saw a women get kicked out for refusing to sit so the children seated behind her could see.
If the enemy team gets a kill and you write 'boooo' in all-chat (or the ever popular 'you got lucky') ... people understand that. If the enemy team gets a kill and you type '%%%got' .. yeah, that's not going to fly.
It's very easy to compartmentalize what we consider acceptable online and in person. For some reason people think they can say anything they'd like online because they are behind a screen. I can guarantee you that if I walked up to you at a bar and started to read some of the chat logs you think are acceptable, you wouldn't receive it too well.