to fuck a girl from behind in her pussy or her ass with her body pressed up against the wall; to hold a girl up wit her legs when fucking and push her against the wall
THE DEFINITION OF "Wallbang" IS: In-game the player has shot at the wall, but despite the wall being...a wall, the opposing team is behind it, so they still get hit.
PERSON #1: "Dude what the hell?!"
PERSON #2: "What happened?"
PERSON #1: "I just got f*cking wallbanged!"