The transition from attack to defence is an important element of football, and applies all over the pitch.
Once posession is lost, the entire team become 'Defenders' instantly. This is an important element to get across to young players who tend to think of defenders as 'the ones at the back'. Defending starts at the front, and starts as soon as posession is handed over to the opposition.

This drill works on the switch between attack and defence. Our players have really loved this drill, as it is fast moving and tiring.

It is worth noting that the first 'runner' in this drill is effectively just part of the set-up, and the drill only really gets going from teh second runner onwards.

Set up a pitch about 20 yards wide and 30 to 40 yards long, with a goal at each end, and a cone about 10 yards from each goal. No goalkeepers. Half your players are to one side of one goal, and half are to one side of the other goal. You should have a number of balls at each end. The first player in each line should have a ball at all times.

The drill starts with the first player from one line running up the pitch and, once he gets past the cone, he shoots at the goal. As soon as he has had his shot, the first player from the second line runs to attack the opposite goal, and the player who has just had his shot becomes a defender trying to stop him.

Players can only shoot once they reach the cone, and they then instantly 'transition' into defensive mode.

The drill then carries on in this fashion. With a player attempting to get to the other end to shoot, and then becoming a defender against the player running from the other end.

You can progress this drill be having two or three runners at a time instead of one, with each becoming a defender once their attack is complete.