In the video, you can see Finnegan jump off the line and hit Johnson who responds by ripping Finnegan's helmet off. Finnegan is able also get Johnson's helmet off but it's Johnson who gets the only clean punches thrown. The referees broke up the fight and both players were ejected.
After the game, Johnson apologized to his teammates for causing a distraction. Finnegan left without speaking to reporters.
It's possible both players face a fine and/or a suspension for their actions. It's not very often that you see a fight in the NFL where the helmets come off and it's like an old-fashioned street brawl.