Wrong Shoulder

"Trapping the Trapper" (as mentioned above) is probably the best way to explain it to the kids (so not to give a negative connotation with "wrong"). The point is trying to take two-for-one with a load / pulling guard. The DLineman / SLB are put in a position to "Trap the Trapper" with down block and keying pulling guard. They aim for the upfield thigh pad, and essentially CHOP the pulling guard. This creates a "cluster" in the backfield, spilling the ball carrier outside.... This takes the FB who was assigned to the end / SLB and the BSG, who was assigned to the inside defender at the point of attack (ILB) out of the picture,giving you a defender free to make the play. The FB assigned to the end / SLB cannot effectively breakoff his bead on the defender, so he will usually try to block a guy that is already blocked / down.

It helps your defenders stay aggressive, yet keep them no deeper than the opponent's heels, working down the LOS.