This is a simple session to deliver to a group of players when looking to develop defensive principles within a back four (This can be manipulated to suit back three’s). Quite simply the reds goalkeeper plays the ball into the yellows who then look to attack the goal in their group of four. Whilst the ball is traveling towards the yellows the reds need to move as quickly as possible towards the ball and look to defend as high as possible.
Once this has happened the practice is very simple, can the reds defend as high as possible keeping the yellows out of the box. As you can see on the wide the different color cones resemble height, the higher the reds can defend the more successful they have been. 

Defending High 

Getting out early will be a key factor in the reds success, the yellow marker represents 25 yards and a mid-block. If the reds are able to force the yellows here then they should be rewarded with three points, then two points for the red zone and one if they win possession behind the red zone. This encourages defending on the front foot, a key factor in this practice. 

Applying Pressure 

It is important that pressure is applied to the ball as quickly as possible, in the example shown here, we are looking for the full-back to become close to the ball and trying to force the player wide (this allows the touchline to become the additional defender). Once the first player has applied pressure we are looking for the player behind the ball to provide cover and balance. This means the second player is in a position to press the next player and cover a run in behind from the ball carrier. 

Double marking plays a key role in defensive movements for teams, develop players here who are comfortable with the principles of double marking.  

For centre-backs or full-backs this is a key session in helping them understand their role and the role of team mates around them.