When a couple breaks up, but before anyone else can pick up the girl on the rebound, the same guy gets back together with her. The term comes from basketball, where an offensive board or offensive rebound prolongs a team's possession.
Man: I heard Katie and Mike broke up. Finally I can get Katie on the rebound, that fox.
Friend: Nope. Mike grabbed the offensive board and got right back with her.
Man: Curses! I'll box out next time.