foul or not
 

A1 takes a shot from the 3 piont line and during his shot B1 tries
to block it. B1 does not foul A1 but when they both land, B1
starts to box out and backs out A1 at the 3 piont line. Is this a
foul or not?

Could be illegal contact, but generally not called as a foul unless A1 is disadvantaged as in knocked down or severely displaced (e.g., could not get the rebound, moved more than a coupla steps, injured or otherwise affected the succeeding play by A1)

Agreed. And, if it is a foul, it's a common foul, not a shooting foul.