A fan at the Anaheim Ducks game on Friday night appeared to be knocked completely unconscious during a wild brawl ... and now, cops say they've launched an investigation into the matter.
The fight broke out as the Ducks took on the Winnipeg Jets at the Honda Center ... when a group of fans who were reppin' opposite teams got into it with each other right in the middle of a concourse.
You can see in video from the scene ... a man in a Jacob Trouba Jets jersey broke off from the squabble and began tussling with a guy in purple Ducks jersey.