Dribbling Up Court

Bear with me as I try to explain this best I can. A1 is dribbling up court after an offensive rebound (fast break situation) and will dribbling up court, B1 is gaining on A1. A1 sort of stops to throw his body/backside into B1 (Sam Cassell does this a lot in the NBA). If B1 knocks over A1, is this a foul on B1, even though he didn't cause it? Also, (for those who understand at all what I'm trying to say) can A1 be called for any foul here?