A cell phone video shows a Los Angeles Rams fan getting knocked to the ground on Monday night by a San Francisco 49ers fan in a Levi’s Stadium parking lot after the 49ers opening night win.

According to an eyewitness who shot the video, the two were arguing, and hurling insults at each other. At one point the Rams fan got close to the 49er fan and knocked him out.

The Rams lost their first NFL season opener in Los Angeles since 1994 to the 49ers, 28-0. The “Monday Night Football” season opener was billed as a national coming-out party for the Rams.

49ers backup quarterback Colin Kaepernick, who has been in the news recently for refusing to stand during the national anthem, was booed when he entered the stadium Monday, but it was quickly replaced with chants of “USA! USA!”

It’s unclear what the argument between the two fans stemmed from, but their scuffle was quickly broken up by onlookers.