Dan Campbell took Brian Branch to task on Sunday night ... ripping his star player for igniting a brawl following Detroit's loss to the Chiefs.
The wild incident occurred just seconds after the Lions fell to Kansas City, 30-17, on Sunday night ... when Branch hit JuJu Smith-Schuster in the mouth for the way he blocked him earlier in the game.
The smack started a melee -- with multiple players from both sides jumping in to try to break things up.
Once the dust cleared, Campbell met with reporters .