On a pass Defender "B", tackles receiver "A" by wrapping arm(s) around the helmet of the receiver, there is no actual "grabbing" of the facemask with the hands but the forearms wrap around the facemask and helmet (see clip below)
https://www.youtube.com/watch?v=FK5b1MN1XvM&authuser=0
is this a foul? Note the play is captured from two different cameras. The flag was for a facemask but this question is not about the facemask flag, but hypothetical that IF the facemask was not grabbed directly, would the tackle have been a foul in anyevent.