hitting on arms during rebound

[SamIAm]

JR,
In your opinion, if the defender has a LGP with his hands at his side, and an offensive player is making a try that extends their arms over the defender, can the defender then raise his arms within his verticality to contact the offensive players arms? The timing is such that the defensive player raising their arms is subsequent to the offensive player's arm being within the defensive players verticality.

IMO - I have no foul if the defensive player's hands are vertical before the offensive player puts his hands or arms within the defensive player's vertical space, but am not sure in the scenario I just described.