This drill starts by reviewing the dip and lean technique and builds on the hoop drill shown here and here. In an ideal world your defensive linemen would do the dip and lean technique, speed right past the blocker and bury the ball carrier before he had a chance to get to the line of scrimmage.
Football is NOT a game of ideal though and the offensive lineman is doing his best to stop the defensive lineman and neturalize the dip and lean. With a little practice and attention to detail, this drill will help your defensive linemen handle any block that comes his way.
When your defensive lineman realized the offensive lineman isn't a pushover, it's time for him to use the "Limp Arm Counter" to continue the rush into the backfield. Using armed dummies this video shows the 3 step technique your defensive linemen need to use to counter the offensive lineman when he stops the rush. Like most defensive line drills, this drill is worked from both the left side and the right side.
Bags are wonderful to work on the basic technique, but working the dip and lean limp arm counter against a real person. This is a defensive line drill, but the guy playing the offensive lineman MUST do a good job so the defenders know what game situations will feel like.