By Dan Durkin

(CBS) The 49ers don’t lead the league in rushing by accident, it’s by design. Offensive coordinator Greg Roman has devised the most diverse running scheme in the NFL, dusting off old running concepts and putting a modern spin on them.

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The 49ers deploy a variety of formations and pre-snap motions to get numerical advantages “in the box.” Combine that with a big, physical offensive line that is nimble enough to get to the second-level, and you end up with a 170-yard per game average.

Preparing for a team like the 49ers is a huge challenge for any defensive coordinator. Traps, dives, sweeps, draws, the 49ers run all of them in the span of a game. In this week’s playbook, I take a look at a few of the creative ways the 49ers run the football.

The situation: On 2nd-and-1 from the Cardinals 41 yard-line the 49ers come out in 2RB-2TE-1WR personnel, and the Cardinals counter with their base 4-3 personnel. The 49ers shift left tackle Joe Staley to the right side forming an unbalanced line, and they have both tailbacks Frank Gore and Kendall Hunter split in a pro set backfield.

The Cardinals respond to the unbalanced line by shifting to an “under” front (the nose shaded to the closed side of the formation).

The 49ers then motion wide receiver Ted Ginn into the backfield drawing the cornerback with him, and hand the ball off to Gore, on a quick hitting “fullback” dive.

With both linebackers shaded to the strong side of the formation, and the back-side defensive end playing contain – following the action of Smith, Hunter, and Ginn – this play comes down to two blocks: one from tight end Vernon Davis and another from guard Mike Iupati. The 49ers win both of these match-ups, springing Gore for a big gain up the middle.

The situation: On 2nd-and 12 from the Seahawks 45-yard line the 49ers come out in 2WR-2TE-1RB with Frank Gore as the lone setback, and the Seahawks counter with their base 4-3 personnel. The 49ers motion Vernon Davis to the top of the formation, which draws safety Kam Chancellor (No. 31) out of the box.

This is an example of the 49ers trap game, which they run better than any team in the league. The 49ers pull right guard Alex Boone to the left, and block down on the Seahawks linebackers with the left side of their line. The 49ers leave defensive end Chris Clemons (circled in blue) unblocked, letting him run himself out of the play, and choose to trap the defensive tackle (circled in green), giving him a free run up the field.

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Boone traps the defensive tackle clearing him out (circled in yellow), the nose tackle is hemmed up by center Jonathan Goodwin, and the second level blocks are secured, allowing Gore to hit the crease with nothing but green grass ahead on a 37-yard gain.

The situation: On 2nd-and-10 from the Bills 47-yard line the 49ers come out in 2TE-2WR-1RB personnel with Frank Gore as the lone setback, and the Bills counter with their base 4-3 personnel.

Quarterback Alex Smith starts his drop like it is a pass play, staring down the Bills linebackers who are blitzing the center gaps.

With six Bills defenders on the strong side of the formation, and the linebackers committed on a blitz, the 49ers run a nifty delayed draw play here, giving Gore two running lanes to choose from. Seeing Nick Barnett (No. 50) in the hole, Gore bounces to the left, following left tackle Joe Staley down the field.

Staley is able to secure a block on the Bills Mark Anderson (No. 93), springing Gore for a 31-yard gain.

This is an example of the 49ers giving the look of a pass play, getting the Bills to commit on the blitz, only to hand the ball off to Gore on a draw.

While Gore doesn’t have the speed to turn these big gains into touchdowns, they move the chains. By giving the defense different formations and pre-snap motions to react to, the 49ers get numerical advantages in the box, and have the lineman to win at the point of attack on pulls, traps and lead plays.

The Bears one-gap philosophy on the defensive line requires lineman to get up the field quickly. Against a team who runs the trap play better than anyone, this could play right into the 49ers hands. The Bears will need their defensive lineman to be aware when they have a free run on a play they’re probably being trapped, their linebackers to get off blocks, and their safeties to play under control in run support, otherwise the 49ers will gash them.

Dan Durkin

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Dan Durkin joined The Score’s columnist community after finishing runner-up in the 2011 Pepsi Max Score Search. He is a graduate of the University of Illinois where he was a member of the men’s football team (despite his best efforts to join the women’s team). Dan is a longtime Scorehead, known as Dan in Wicker Park – even though he no longer resides in Wicker Park – who will be sharing NFL analysis and opinions. You can follow Dan on Twitter @djdurkin. To read more of Dan’s blogs click here.