Backside bunch is an attacking corner kick play where a group of players forms a mob at the top of the box before running to different areas when the kick is taken.
Create a corner kick situation with an attacking and a defending team. It may be best for the offensive team to practice without defenders the first few times but then you'll want both.
The offensive team sets up with a kick taker, one player in front of the goal keeper, and a cluster of players outside the corner of the box on the opposite side of where the kick is being taken.
The players in the cluster plan out where they are going to make their runs into the box ensuring that they are running to different areas. Front post, back post, penalty spot, and top of the D, are all good areas players can say they will make their runs to.
Before the kick is taken the players run around randomly in the mob to try to lose their defender and give themselves space. Right before the kick is taken they begin their run in to the area they chose and try to score once the ball comes in.
Timing of the runs is very important so be sure that the players are arriving where they want at the same time the ball is.