Transcript for Seattle Seahawks Crowd Violence Prompts Undercover Investigations
fans heading out the football games on this sunday. They know the harsh reality. Sometimes the tackling is not just down on the field. Fighting in the stands is getting out of control. Sbrees increasingly, it's captured on youtube. Neal consider lynn ski has more on the story. Reporter: It's sunday. It's september. And that can only mean one thing. It's game time. Reporter: Football. But at too many games, that's also meant this. Get back, now! Reporter: Violence. Fan versus fan. All over youtube. Often brutal. And often just because someone is cheering for the wrong team. Everybody likes to root to their team. But we're tired of the violence. Reporter: The nfl is tired of it, too. And wants people to know it's doing something about it. Today in seattle, while the game is in motion, the seahawks have arranged for undercover police to be in the stands, working a sting as creative as it is unusual. They'll be dressed in the visiting team's colors, acting as bait and a deter rent. Plain clothes officers wearing opposition jerseys. People don't know where the police are. When they don't, they're more likely to be on thiz best behavior. Reporter: Fans being disruptive or on scene can be kicked out and forced to take a four-hour online course before being able to buy a ticket. Fans fed up with the violence welcomed the fresh idea. There are knuckle heads out there. They're going the make sure the nuk knuckleheads pay for what they do. Reporter: For "good morning america," neal karlinsky, abc news, seattle. We're going to get a didn't
This transcript has been automatically generated and may not be 100% accurate.