Crazy scene following a Premier League game on Thursday ... ex-soccer star Patrick Vieira -- who now manages Crystal Palace -- kicked a fan in a wild altercation on the field.
It all went down after C.P. lost in heartbreaking fashion to Everton ... when a bunch of Toffees supporters stormed the pitch to celebrate their team's big win.
At one point in the chaos, one of the fans appeared to taunt Vieira -- and an altercation quickly ensued.
You can see in video, Vieira grabbed the man, took a swipe at the fan's face, and then kicked him so hard in the leg -- he fell to the turf.