Duff up
Definition 1 of 2
Pro Tip 1/3Violence implied
The phrase suggests physical harm, used in serious or threatening situations. 
If you cheat again, they might duff you up after the game.
Pro Tip 2/3Intensity varies
Can mean minor to severe beating, depending on context. 
He got duffed up a bit during the scuffle, nothing too bad.
Pro Tip 3/3Informal slang
It's slang, so it's not appropriate for formal contexts. 
I wouldn't use 'duff up' in our report to the board.