1. rude slang To physically attack one, as with punches and other blows, such that they suffer significant injury. This phrase can be used both literally and hyperbolically. Our neighbor is in the hospital because a burglar knocked the shit out of him. I'm worried that the captain of the football team will knock the shit out of me if he finds out that I'm secretly seeing his girlfriend. Oh, my boyfriend knows that I would knock the shit out of him if he ever lies to me about something that serious.

2. rude slang To defeat one decisively in a competition. The final score was 17-1? Wow, we really knocked the shit out of that team! I was doing pretty well for most of the tournament, but Sara knocked the shit out of me in the semifinals.