Washington Redskins head coach Mike Shanahan found a diamond in the sixth-round rough when he selected Florida Atlantic running back Alfred Morris 173rd in the 2012 NFL draft, but don't call it a fluke.

Maybe even Shanahan didn't expect Morris to rush for a team-record 1,613 yards as a rookie and outgain every back in the league not named Adrian Peterson. But history is certainly on Shanahan's side when it comes to taking less-than-blue-chip backs and turning them into extremely productive studs.

Since being hired to coach the Denver Broncos in 1995, Shanahan has groomed seven different 1,000-yard backs, none of whom were drafted in the first round. Combined, those backs posted 12 1,000-yard campaigns.

There was that now-famous Terrell Davis pick in Shanahan's first draft in Denver. Davis, who was the 196th pick in Round 6, was drafted after 17 other backs. But the Georgia product went over the 1,000-yard mark in each of his first four seasons, finishing second to Barry Sanders in the race for the rushing crown twice and winning it with the fourth 2,000-yard season in NFL history in 1998.

Injuries caught up to the Super Bowl MVP after that, but that didn't hurt the Broncos' running game as much as you'd expect.

In 1999, Shanahan found Olandis Gary with the 127th pick in Round 4. At that point, 11 other backs had already gone off the board, but Gary—who also came from Georgia—outran all but one of them in his rookie season, finishing behind only No. 4 overall pick Edgerrin James with 1,159 yards.

Gary got hurt the next year, but that didn't matter because Shanahan returned to that Round 6 well in the 2000 draft, grabbing Mike Anderson with the 189th pick. Sixteen other backs had been chosen before the Utah product had his name called, but Anderson outran every single one of them with 1,487 yards in his rookie season.

Anderson was the league's fourth-leading rusher that season, and he'd hit the 1,000-yard mark again a few years later.

Then came Clinton Portis, who was the only one of those 1,000-yard backs taken on the first day of the draft. Portis was a second-round pick in 2002, but he still went off the board after three other backs. The Miami product finished fourth in the NFL with 1,508 yards as a rookie in 2002, and he followed that up with a 1,591-yard performance in '03.

And yet the Broncos were so confident in their ability to find backs that they traded Portis to the Redskins two very successful years into his pro career.

For a while there, it really seemed like anybody could step into the Broncos backfield and dominate. Reuben Droughns came out of nowhere to finish in the top 10 in rushing in 2004. In '05, Anderson and 2004 second-round pick Tatum Bell combined for 1,935 yards, with the Broncos finishing in the top five in rushing yardage, yards per carry and rushing touchdowns.

Shanahan got by during the twilight years of that Denver era with guys like Peyton Hillis, Selvin Young and Mike Bell. It didn't matter—nobody messed with the Broncos on the ground.

And now here we are in D.C., where Morris has already become a star. Yet only a year ago, in Shanahan's second season with the 'Skins, co-rookie sensations Evan Royster and Roy Helu were the talk of the town after combining for 968 yards (which would have led all first-year backs in rushing) while averaging 4.7 yards per attempt.

Does Shanahan see something we're all missing? He clearly has a special ability to find backs under rocks, but there's more to it. Let's break down the magic.

Hint: It has something to do with the zone-blocking scheme

That's something Shanahan implemented immediately when he arrived in Denver. In that first year, he teamed up with offensive-line coach Alex Gibbs, who also worked for Shanahan in the same role in Los Angeles in the late 1980s, and that coaching duo became the face of zone blocking.

The concept itself is so simple that it's almost self-explanatory, but it requires a lot more from the players involved than a regular running play. The idea, of course, is that instead of taking the nearest defensive player on a running down, offensive linemen and tight ends are instead responsible for zones. They have to move quickly and move laterally, and they have to keep moving.

It lends itself to more double-teams, with one of the two double-teaming linemen quickly releasing to pick up a defender in the next level. That means linemen have to work in each other's space, which means they have to be on the same page at all times. Who will release, and who will stick? There's no room for error, but the payoff can be huge.

How huge? Shanahan has coached 17 seasons since joining the Broncos. During the same span, Tom Coughlin and Jeff Fisher have the same number of campaigns under their respective belts. Bill Belichick has coached 18 seasons since 1991. Those four are the most experienced active NFL head coaches.

Let's compare all four in terms of success on the ground, leaving out Belichick's first year in Cleveland just to keep that 17-year time line across the board.

It's a landslide. Yes, I realize that not all offenses operate in the same way, but it's not even like Shanahan is known as a conservative, run-first offensive schemer. Don't forget that the guy had John Elway, too.

And yet he's had a top-five rushing attack in 10 of his 17 seasons (and top 10 in 13). Those other three coaches have only finished in the top five in rushing yards eight times in a combined 51 seasons.

And aside from a small blip in his first couple seasons with the rebuilding Redskins, his head and shoulders have remained consistently above those three on a year-by-year basis in terms of yards per carry.

Gibbs left Denver to join the Atlanta Falcons in 2004, bringing the zone-blocking scheme to the NFC South. There, the Falcons led the entire league in rushing yards and yards per carry for three consecutive seasons.

From there, Gibbs landed in Houston, where he and fellow Shanahan disciple Gary Kubiak implemented the zone-blocking scheme in which Arian Foster is still rocking out today. The Texans have finished in the top eight in the league in rushing each of the last three years.

In fact, offenses Gibbs has worked with have finished in the top five and top 10 in rushing more often than Shanahan-led attacks. Foster went undrafted out of Tennessee, but he's run for more yards than any back in football except Peterson since 2010.

But why doesn't everyone run a zone-blocking scheme?

Many teams do, to various degrees, including the Colts, Chiefs, Seahawks, Packers, Dolphins, Steelers and, of course, the Redskins and Texans. But there are several reasons only a few teams can successfully pull off a heavy zone-blocking offensive approach.

First, you need the right linemen. It's a lot easier to find big, slow dullards than it is to find offensive linemen who are smart, nimble and technically sound. That is a requirement here. Since zone blocking involves a lot of double-teams, sheer size and/or strength isn't enough to get by in this scheme.

It's simple: There aren't enough quick, alert linemen out there for everybody to zone block successfully.

Here's a fairly standard running play compared to a zone-blocking run play. The difference is significant.

Secondly, cohesion is essential. In a speech on zone blocking transcribed by Bud Elliott at Tomahawk Nation, Gibbs noted that zone-blocking offenses "don't want guys who miss games, because of the importance of continuity."

That's exactly what he and Shanahan had in Denver...

Look at the Redskins' line now. It was still ironing some things out in Shanahan's first two seasons, but in 2012, all five regulars started all 16 games until right tackle (and weak link) Tyler Polumbus missed the regular-season finale.

The 'Skins probably wouldn't have finished with the league's top-rated running game had it not been for that continuity.

Shanahan found these guys. Left tackle Trent Williams was his first draft pick in D.C. He signed right guard Chris Chester, who was tailor-made to perform as a zone-blocker. He drafted left guard Kory Lichtensteiger in Denver and brought in Polumbus as an undrafted free agent. Center Will Montgomery is the only starter Shanahan didn't handpick and groom.

These linemen are findable and signable, but Shanahan and Gibbs have proved they are experts at finding them. And almost as importantly, they've made the effort. It's 2013, man, and front offices aren't necessarily focused on players who best suit niche run schemes. Pass protectors take precedence in this pass-happy league, and thus not everybody is competing with Shanahan, Gibbs and Kubiak for these specific types of players.

You need a special kind of running back, too

This applies to the logic regarding why not everyone runs a zone-blocking scheme, but it's also a major factor behind how and why Shanahan generally continues to—as the title suggests—churn out running back success.

Not only do you need the right kind of linemen to make a zone-blocking scheme work, but you obviously need the right back.

Notice we didn't say "best" back. That's precisely why Shanahan keeps finding these guys in football Siberia. He's not looking for beasts, and he'd be silly to pay big bucks for one. He wants and needs smart, one-cut runners who can see the field and anticipate holes in the fog of war.

You can't excel behind zone-blockers if you're not supremely patient and you don't possess top-notch vision. Simply put, you have to be smart. Darren McFadden might not be an idiot, but he's a straight-ahead smasher, and we got proof last year in Oakland that he's not suited for a zone-blocking scheme.

Morris and Foster fit the bill.

From Grantland's Chris Brown:

Gibbs' style of zone blocking requires total commitment by every offensive player—linemen must be perfect technicians, not just fat guys who push others around; runners must make reads and make "one-cut-and-go" plays rather than juke and tap dance like the next Barry Sanders; and quarterbacks and receivers can't treat runs as mini-breaks because they're expected to execute assignments and make blocks. The offense is also taxing on coaches. Gibbs will tell anyone willing to listen that if you want to be good at the wide zone and the tight zone, throw out all of your other run plays.

Which leads us to coaching ability

How do you get a bunch of overgrown children to put their egos to bed and listen to you? That's the challenge NFL coaches have been dealing with while trying to hold the attention of 20-something-year-old millionaires for decades, and doing so is even more difficult when you're trying to get them to grip a zone-blocking scheme, which requires a tremendous amount of focus, hard work and discipline to master.

Is it easier to make a sixth-round pick listen to you? Absolutely, and that's a big reason all of the elements of the Shanahan/Gibbs system have come together successfully. Not only do they not need superstars, but they really don't even want them.

Wrote Elliott:

You'll recall that the Broncos traded Clinton Portis away for Champ Bailey, in large part because they valued a corner over a runner, but also because they knew they could find another runner to function within their machine.

It isn't easy to teach eight or nine guys to work in unison, period. Shanahan has found a way. Gibbs, too, but as Brown pointed out he's been forced to jump around the league a bit.

While the draft sometimes feels like a crapshoot, especially in the later rounds, Shanahan hasn't simply gotten lucky over and over again. He's handpicking linemen and backs who suit his scheme, he's hiring them, he's grooming them and he's producing ground success at a rate that doesn't seem possible in this ultra-competitive league.