1. To put constant forceful pressure on someone or something. People kept pushing up against me from behind while I was trying to watch the show. I can't open the door because something on the other side is pushing up against it.

2. To press, shove, or thrust someone or something in forcible contact with someone or something else. In this usage, a noun or pronoun is used between "push" and "up against." The bully pushed Billy up against the wall and threatened to steal his lunch money. Someone pushed a table up against the door from the other side so no one could open it.