Whenever I play middle back on defense I always try to do two things...
- Follow the set...
- That sides front and middle players go up to block leaving short open. That side's back row player will usually pull up to cover short, leaving deep open. Opposite front row player will pull back and play short cross. Back row player on opposite side of set will pull back for deep cross.
- By positioning yourself with a foot on the line when following the set, you only concentrate on moving left & forward or right & forward... depending on which direction the set went.
- Position yourself to see the hitter...
Think of it as a pulley system... pretend to attach bungies to the players on defense. Ideally all three front row players will be at the net on defense initially. When the set is made, whichever front row player is not blocking will pull off leaving more slack on the line and pulling the defense around to the side the set is going. If you put up a triple block against the middle, that will pull up both outside backrow players to cover the short cross hits.