Definition

Canadian (especially hockey) slang: to engage in gritty, hard-nosed play—battling and grinding, doing the dirty work; more broadly, to roughhouse or stir up trouble.

Examples

"He’s the kind of winger who loves to muck in the corners, winning puck battles and wearing down the D."

"After the whistle they started to muck it up in front of the net, lots of shoves and face washes."

"Quit mucking around downtown after the game—you’re just stirring up trouble."