I would have had B1 for the arm grab prior to A1's travel.
(beat you to it
JAR 
)
As for the block/charge aspects, B1 moves into A1. It was a feat for him to even get in front of A1 at all considering B1 was going the wrong direction when A1 started his drive.
B1 in this play may be the quickest basketball player I've ever officiated.