Here is the rule for permissible contact:
ARTICLE 3. PERMISSIBLE ACTS BY BOTH TEAMS WHILE THE BALL IS IN THE AIR
Acts that are permissible by a player include, but are not limited to:
- Incidental contact by an opponent’s hands, arms, or body when both players are competing for the ball, or neither player is looking for the ball. If there is any question whether contact is incidental, the ruling shall be no interference.
I have read all the comments about Shepard leaving his feet and taking a peek at Diggs before contact and this, I think, is easy to understand. Shepard did see Diggs coming at the last minute and the leap was an attempt to avoid contact. If Shepard intended to block Diggs, why leave his feet? I think it was an instinctive move.
In any case, the rule says if there is any question whether contact is incidental then the ruling should be no flag. I do think there is a question about this play, as we are debating it after the game. But when bodies fall to the ground, refs like to throw flags. I am surprised they didn't call it PI against Diggs for impeding Shepard's route.
And btw, if the receiver sees the QB in trouble it is normal for them to turn back to the QB to get open. So the fact that he curled back is not significant to me.
But, I can see the refs calling it either way based on the rule. The non-calls against Noah Brown were much harder to explain. They were clear violations of the rules.