Running backs continue to evolve

Mikel Leshoure and Jahvid Best will share carries depending on the defense the Lions are facing. Getty Images

Jim Schwartz, the bright coach of the Detroit Lions, made an interesting post-draft comment explaining why the Lions selected Illinois running back Mikel Leshoure in the second round.

Leshoure will become the Lions' big back, a 6-foot, 227-pound rusher. His selection came a year after the Lions used a first-round pick on Jahvid Best, who's explosive and quick at 5-10 and 199 pounds. Schwartz's explanation is another illustration of how the running back position is evolving.

"There's a lot of different things that happen in our division," Schwartz told Lions reporters after the draft. "We see a 4-3 team like the Chicago Bears. We see a 3-4 team like the Green Bay Packers.

"That's a different style of running back. You play 3-4 teams that are two-gapping, you need a big back who can run through some arm tackles. You want to get guys matched up on different teams, you need guys who can match up and beat linebackers and people that want to play man and trick coverage up for a certain player."

It's been fascinating to watch the game change for running backs, especially in the past decade. In the 1970s, the game belonged to the runners. Quarterbacks had to stand down and accept their coaches' plans to run the ball and win with defense. Pittsburgh's Terry Bradshaw and Miami's Bob Griese were among the Hall of Fame quarterbacks who often threw fewer than 20 passes a game.

Lately, particularly after Peyton Manning entered the league in 1998, the game has shifted to the quarterback. Now, 59 percent of offensive plays are in the passing game, and coaches have started mixing and matching running backs. Some teams use two backs; others use three.

The ideal of having one featured back has diminished in recent years to the point where only six backs in the league averaged at least 20 carries per game last season. Schwartz's observation about backfield matchups is right on if you look at some running back stats, particularly in an age in which 3-4 defenses have re-entered the league.

Fifteen teams ran 3-4 schemes last season. The Browns and Broncos have switched back to four-man lines, but the Houston Texans went to Wade Phillips' 3-4 this season, setting the current number of 3-4s at 14.

Accepting that some 3-4 conversions have failed, it's hard to pull up leaguewide trend stats. Everyone knows how hard it is to run against the Steelers' and Ravens' 3-4 schemes. In Cleveland, though, two head coaches lost their jobs trying to establish a run-stopping 3-4. Mike Nolan couldn't consistently stop the run in San Francisco using a 3-4. The Jets struggled until Rex Ryan took over. Denver's switch turned out to be a failure, too.

What's clear, though, is that Schwartz is correct. To beat a 3-4 defense on the ground you need a bigger back, or at least a runner who can break arm tackles.

No back in the NFL breaks arm tackles better than Adrian Peterson of the Vikings. He's 6-1, 217 pounds, and he runs with a vengeance. But as great as he is, his numbers have dropped trying to slug his way through an increased schedule of 3-4 defenses.

Peterson had his best season in 2008, rushing for 1,760 yards and averaging 4.8 yards per carry. However, his numbers dipped during the next two seasons with Brett Favre in town and more 3-4 defenses on the schedule. In 2009, Peterson faced seven 3-4s and rushed for 1,383 yards. Last season, he had eight 3-4 games and rushed for 1,298.

Because he can break arm tackles, Peterson maintained impressive yards-per-attempt numbers (4.4 in '09, 4.6 in '10), but it was clearly tougher going against more defenses in which linemen were two-gapping against blockers and linebackers flowed into holes to stop him.

Ray Rice is a 5-8, 212-pound star for the Baltimore Ravens, and he faces the supreme challenge of playing in the AFC, which features nine of the league's 3-4 defenses. Rice opened last season with seven of eight games against 3-4s.

Having a 133-yard game against an overmatched Denver defense helped, and Rice rushed for 606 yards and averaged 3.9 yards per carry during those first eight games, but his average against the 3-4 defenses was 3.82.

Likewise, the Steelers got at least 1,200 yards from Willie Parker, 5-10 and 212 pounds, each year from 2005 to '07, but he wasn't as effective breaking arm tackles. That forced the Steelers away from their normal, run-dominated offense.

A bigger Rashard Mendenhall has helped re-establish the Steelers' running attack when they want to feature it. Fellow AFC North team Cincinnati would be lost if it didn't re-sign 5-11, 227-pound Cedric Benson, who, like Mendenhall, can break arm tackles.

For what it's worth, the decision by the Buffalo Bills to take 5-11, 196-pound speed back C.J. Spiller looks even more curious now than on draft day 2010. Spiller is in a division filled with 3-4 teams -- New England, Miami, New York Jets -- and plays in a conference dominated by two-gapping 3-4 defenses.

The NFC does allow for more matchup flexibility, which plays to Schwartz's theory. Unless the NFC teams draws the AFC East (four 3-4 teams), NFC coaches can formulate game plans that lean on bigger backs against 3-4s and quick backs against 4-3 teams.

In Detroit, Schwartz can use Leshoure's strength and power to attack the Packers' 3-4 scheme, then shift to Best's speed to outrun the 4-3s played by the Vikings and Bears. Getting Leshoure was a nice luxury in Detroit and a good example of the evolution of running backs in response to defensive changes.

John Clayton, a recipient of the Pro Football Hall of Fame's McCann Award for distinguished reporting, is a senior writer for ESPN.com.