[Capt. Tom]

(a) Contact by a defender who is not playing the ball and such contact restricts the receiver’s opportunity to make the catch.

That's what I saw - throw the flag. -Tom

[DBCJR]

You didn’t see the receiver grabbing the defender’s face mask? The defender, at that speed & angle, was controlled by the receiver at that point. The receiver PULLED him into himself....

AND the defender could NOT play the ball.

Furthermore, the pass was uncatchable because the QB hit the defender in the back.