This article originally appeared in 2006. It is still a good one.
by Brian Hook, FootballOutsiders.com
Denver running backs seem to remain Denver running backs for life ? possibly because they have a nasty habit of suffering devastating injuries while a Bronco. Terrell Davis, Mike Anderson, Olandis Gary, Reuben Droughns, Quentin Griffin, and Tatum Bell have had almost all of their career carries as Broncos. The only player in recent memory that has gone from Denver to another team and achieved significant carries in both locations is Clinton Portis.
Zone Blocking
For those of you unfamiliar with the Denver offensive line scheme, they use a technique known as "zone blocking". In a "man" or "drive" blocking scheme the lineman is responsible for an individual, and the play is designed for a running back to hit a particular gap. The zone blocking scheme, on the other hand, has a lineman blocking an area instead of a designated defensive player. If multiple linemen are blocking an area than one can break off and block into the second level.
The offensive line typically moves as a unit laterally, and the result of their blocks should create some natural seams or gaps in the defensive formation. The running back is responsible for finding a hole, making a cut, and then running upfield. One of the key tenets of the Denver system is that the running back takes what he can get ? he should never dance around waiting for a hole to open. He needs to be agile, authoritative, and possess good instincts. Nothing fancy, just try to gain positive yardage.
A final element of the zone blocking scheme is the use of the much hated cut block to seal off backside pursuit. This means that any linemen on the backside of the play cut block defensive players in front of them, which drops the defensive players to the turf and, oddly enough, opens up holes for the running back. Note that the cut block is legal in this case, as long as the offensive lineman isn't hitting the defender from behind and as long as he doesn't roll up on his legs. But hitting him below the knees near the line of scrimmage is fair game, as much as the NFLPA doesn't want it to be.
Obviously getting defenders on the ground is one benefit of the cut block, but an intangible benefit is that defenders start worrying about their knees and ankles. They lose a bit of their aggression and speed since they're paranoid that some lineman is going to creep up on them and take out their legs. This has the benefit of slowing down the entire defense.
For the record, Joe Pendry claims that his zone blocking scheme doesn't rely on cut blocks. Given Davis's performance, he might want to reconsider that stance.
Summary
The "Denver system" isn't a magical pill that a team can swallow to generate 1500 yard rushers with consistency, but obviously it has been successful for running backs in Denver. One reason it has not been widely adopted is time: it takes time to teach, time to master, and time to get the smaller, more agile offensive linemen that the system requires. If you take zone blocking and try to implement it with 340 pound behemoths, you will probably fail, and for better or for worse, 340 pound behemoths are what you'll find on a typical offensive line in the NFL.