Bum rush

When you bum rush someone, it means you ambush them using an unfair combat advantage. A lot of the other definitions list it specifically as charging someone and bodyslamming them into a solid wall, which is applicable because it's total bullshit and usually catches the victim off guard. Other examples include (but are not limited to) attacking someone from behind by sprinting at them and landing a tackle, ganging up on someone and beating them to the ground with superior numbers, or hitting someone with a sucker punch while they're distracted fighting someone else. This is also a tactic in the board game risk, but in this case it consists of plopping down all your armies in one previously weakly defended country and defeating the surrounding countries (usually defended by only 1 or two armies) by spam attacking and having your opponent be unfortunate enough to roll a 1 every goddamn time and lose half their territories. Smash and grab robberies could be considered another example, as a mob of people obscure their faces, run into a store, grab whatever they can, and dash out in the blink of an eye, using their superior numbers to overwhelm store security and staff and to make it harder to uncover an individual suspect's identity. Bum rushing comes from the fact that these tactics are often seen as cheap or low of someone to use, which makes them a bum for having to use them instead of a fair fight.