Really? Did Shanklin prevent a tackle being made on North or is the issue that Shanklin ran ahead of the ball and contacted a defender? (Are you looking at a still or a video?)
De Villiers committed himself totally to Shanklin, De Villiers could do nothing about North's run, none of the Bokke backline picked North up. M. Steyn was too late getting across, would not have made the tackle and was obstructed by De Villiers not by Shanklin. Obstruction would've been a very harsh call IMHO but I've seen that call made.
Error in Bokke defence for me, Shanklin was Steyn's man, De Villiers should've picked up North. Great try!