IMHO, the covering official would need to rule that the A wing was not considered a blocker. Our rule of thumb is : If he's side-by-side or turned away from the D back, he's not.
Those are valid ‘qualifying’ statements. In this specific instance, though, ain’t no way he can be considered a ‘blocker.’ The first move the split receiver (not a ‘wing’) made was a half-hearted ‘swim’ move with his right arm in a clear and obvious attempt to get around the defensive back to continue his pass pattern. But, the defensive back then grasps the receiver with both hands and pulls and twists the receiver, which causes the receiver to stumble slightly. Then the defensive back finishes off the receiver by shoving him to the ground with his left hand/arm. That was NOT an effort to ward off an opponent who was blocking/attempting to block him. The defensive back then looks back to the QB, and, lo and behold, the ball is thrown right toward the area where the receiver would have been, had he not been grasped, pulled, twisted and shoved to the ground. That, my friends, is a foul under anybody’s rules.
The ball was not in the air before the receiver was fouled, so this is defensive holding, rather than pass interference. But, a foul, nonetheless, which, as you say, would offset the live-ball illegal interference foul by the Team A squad member. (Same for NCAA, by the way.) In a crew of 5, the Back Judge must get this. In a crew of 7, the deep wing on the receiver’s side of the field must get this.
