Blind screen help

[kycat1]

Am I wrong or right?

Player A1 has ball top of key with Player B1 guarding. Player A2 comes up right behind B1 to set a screen for A1. A1 breaks for basket and B1 tries to go with A1 but is impeded by the blind screen. No big contact but small B1 is stopped by bigger A2 being right behind him. I call an illegal screen on A2 (did not give 1 normal step since it was a blind screen) and give the ball to Team B.

At half time, my partners say that I should not have called a foul on A2 because A2 went right up to B1 and made slight contact so therefore B1 "knew" he was being screen by A2 because he could feel his body on his back. Since he knew he was there, it was now B1's responsibility to go around A2 without making hard contact.

I think a blind screen from behind wheter or not you touch the player is still a blind screen and you must give that 1 normal step.

Right or wrong? I can find nothing in the case book (4.40) about screening.