A 1987 recording by the rap group Public Enemy popularized the slang term “bumrush” as a verb meaning “to crash into a show hoping to see it for free,” evidently by analogy with an earlier usage in which it meant “a police raid.” In the hip-hop world to be “bumrushed” (also spelled as two words) has evolved a secondary meaning, “to get beaten up by a group of lowlifes, or ‘bums’.” However, older people are likely to take all of these as mistakes for the traditional expression “bum’s rush,” as in “Give that guy the bum’s rush,” i.e. throw him out unceremoniously, treating him like an unwanted bum. It was traditionally the bum being rushed, whereas in the newer expressions the bums are doing the rushing. It’s good to be aware of your audience when you use slang expressions like this, to avoid baffling listeners.
Side note: Britons laughed themselves silly when they saw Americans wandering around in sportswear with “B.U.M.” plastered in huge letters across their chests. “Bum” means “rear end” in the UK