Roll tackling is a way to tackle the legs of a ball carrier under 2 specific circumstances: (1) the over sized, physical back bearing down on the tackler, and (2) making a play in pursuit as the ball carrier is running away from your player.
The roll tackle is a great way to combat a physical back who will either lower the shoulder and attempt to run over tacklers, or use the stiff arm to keep tacklers from getting to him. The physical stiff arm is difficult to combat in any other way. I have heard coaches talk about swating the stiff arm down and them tackling, but I have yet to be able to teach that to a player and see it in action on game film. The best way to combat this issue is to roll tackle, so that the stiff arm cannot reach the tackler in the first place.
It is also effective in attempting to run down the ball carrier in pursuit. The pursuit that we all spend so much time on is only good if it results in a tackle- so why not give kids a tool to use when they are running someone down in pursuit?
Note that the roll tackle is not simply "diving at legs" or "cutting' the ball carrier, but a method to shoot hands, wrap up, and finish the tackle, just as we would expect every tackler on the defense to do. We call it the roll tackle becasue of the action of the tackler's body when he executes this tackle.
Players should punch their hands, just like on any other tackle, once the hands are around the ball carrier's legs, they should be squeezed to the chest, tucking the shoulder in. This creates a scenario by which the tackler rolls and bulldogs the ball carrier, increasing the likelihood that he will go to the ground.
To talk about ways to drill this tackling, use the "Contact Coach Albers" tab or Email
(Film of the roll tackle is available on my youtube site: search coachkeithalbers or http://www.youtube.com/user/coachkeithalbers?feature=mhum)