How much can ball handler use his arm?

[bob jenkins]

Originally Posted by potato

So meaning A1 has the right to defend his verticality with his body/arm,

what if:

A1 did not extend his arms into B1's vertical however pushed B1's extended arm away (within A1's verticality) and makes B1 fall down or cause B1 to be displaced while on air?

A1 initiate contacts with B1's extended arm within A1's verticality, would B1 be called for a defensive foul? For example B1 extended his arm towards A1 A1 raises arm to block B1 continues pressing his arm towards A1's blocking hand.

As I'm seeing these plays in my mind, both are either fouls on A or no calls.