Having recovered off the serve and now facing a good return back deep down middle to his forehand, see Murray's movement and use of his feet during the shot. He loads in a semi-open stance, though his linear momentum is still at work taking him backwards. He therefore uses a backwards hop step (take off on right foot, land on right foot), which enables him to maintain dynamic balance and in this case (determined by his choice of shot), limit upper body rotation which allows him a steeper racket path and closer contact point to play a heavier/higher neutralising ball.
Had he selected a more aggressive shot intention, he might have used a backward pivot or backward jump (ie: landing on his left foot) which would have distanced his contact point, increased shoulder rotation and body speed and flattened his swing path.
A nice example of how footwork provides the right environment for body work, and how body work creates the right environment for racket work.