contact on a blind screen

[Ang]

Here's the situation. NF rules. B1 is guarding dribbler A1. A2 sets a legal blind screen on B1, allowing for time and distance. B1 makes SEVERE contact with the screener A2 displacing the screener A2. A2 ends up on the floor. B1 did not see A2 in his peripheral vision. What's the call ? Is it a no call, Incidental contact? Or a pushing foul on B1 for displacing A2 even though he did not see B1.

Thanks

Ang

Ontario, Canada