If Targett is guarding air, that doesn’t necessarily mean he is out of position, depending what is happening in play at that time. Depending on the phase of play, i would expect my full backs to be guarding air sometimes. For example, if the ball is wide on one side and the defender had shuffled across from their original positions, I’d want my opposite side full back to be in space (air), and away from any player wide on the opposite side of the pitch to the ball. You may have meant the opppsite (that he stays out on his own flank)