In some [tag]football defense plays[/tag], it is important to break the timing of [tag]receivers[/tag] and quarterbacks by jamming them at the line. 
What you need – At first, you can just have two lines of defensive backs and linebackers with coaches and tackling dummies until the players learn a good technique for the jam. Add real receivers once the jam is perfected.
How this drill works – When the ball is snapped (or the play begins) the defensive back, instead of beginning a backpedal, with step forward like he is going to make a block, and engage the wide receiver.
While the set up is similar to a block (because you need a solid base, or you will get knocked over), the contact is hard, brief and more to cause annoyance to the player, rather than to wrestle him to the ground.
The idea at first would be just to give a quick jam, under the shoulder pads at the chest, and then to get into your backpedal, or to open the hips and start side sprinting with the receiver.
Result – If you can execute a good jam, your [tag]football[/tag] players will cause havoc with a team that works on timed passing routes.
