DB is playing off coverage and sidestepping BACKWARDS. Based on this coverage the WR should have run a 15yrd stop and out, but he does not. He's looking to his right and not even looking for the ball. he does not stop. He doesn't even really look back for the ball. Had he stopped like he should have he would have had a chance to make the catch since the DB was playing off ball. Now it may have been a bit high and not really a back-shoulder throw but it would have put the WR in position to make the catch