James Tarkowski's foot made contact with Sean Longstaff's head.
There is no question about that, so you can make an argument for a penalty for Newcastle.
But it is clear from the replays that Tarkowski did not know Longstaff was behind him when he made his clearance.
He cleared the ball and Longstaff threw his head in.
It was a subjective call.
Referee Anthony Taylor did not see it as a foul in real time, and VAR Stuart Attwell backed his on-field official in deciding Tarkowski should not be punished for the follow-through of his clearance.