File-This Jan. 21, 2018, file photo shows Minnesota Vikings' Jerick McKinnon running past Philadelphia Eagles' Ronald Darby during the first half of the NFL football NFC championship game in Philadelphia. The 49ers agreed to a four-year contract with versatile running back McKinnon and a five-year deal with interior offensive lineman Weston Richburg on Wednesday, March 14, 2018 just after the start of the new league year. McKinnon will replace starter Carlos Hyde, who was allowed to leave in free agency.(AP Photo/Matt Slocum, File)

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It was one of the most surprising deals of the 2018 free-agency cycle, and it could be one of the most productive. 

When the San Francisco 49ers signed former Minnesota Vikings running back Jerick McKinnon to a four-year, $30 million contract with $15.7 million guaranteed and a $2 million signing bonus March 14, it seemed like a lot for a guy who had gained just 1,918 yards and scored seven rushing touchdowns on 474 carries over four seasons in Minnesota.

McKinnon’s 142 career receptions for 984 yards and five touchdowns spoke to his versatility, but one may wonder why the 49ers would pay so much for a back whose skill set could be found in the draft. After all, couldn’t USC’s Ronald Jones II or North Carolina State’s Nyheim Hines provide the same relative, versatile production in a speedster’s frame with a second- to middle-round pick for less money?

Kyle Shanahan, the 49ers’ head coach and offensive play designer, would disagree. It was clear in the press conference announcing the signing that what he saw of the 25-year-old’s tape made McKinnon the perfect Shanahan running back.

“There’s so many things I liked about him, just visualizing how I would use him and the stuff that we would do,” the coach said last Thursday, per Matt Barrows of the Sacramento Bee. “Even though there wasn’t a ton of it, you’ve still got to see him do some stuff that we do a lot. And whenever he did, he excelled a ton and looked very good at it.”

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When you watch McKinnon’s tape and look at what Shanahan did as the Atlanta Falcons offensive coordinator in 2016, it’s easier to see not only why the 49ers found McKinnon so valuable, but also how he’ll be used. In 2016, Shanahan led the NFL‘s highest-scoring offense. He did so in part by deploying running backs Devonta Freeman and Tevin Coleman in creative ways. If sharing the field, the duo might’ve started in the backfield together—or one in the backfield and one in the slot—and would align through pre-snap motion to exploit advantageous coverage matchups, particularly against slower linebackers.

This is essentially how former Vikings offensive coordinator and current New York Giants head coach Pat Shurmur used McKinnon in 2017, when he gained 570 yards and scored three rushing touchdowns on 150 carries. He also had 51 catches for 421 yards and two more touchdowns. McKinnon took the same screen and swing passes you’d expect from any other running back, but when Shurmur got creative with him, the results were often dynamic.

“What is a huge bonus on him is when you talk about the pass game,” Shanahan said at the press conference. “When it comes to separating and beating linebackers and safeties in man-to-man coverage, I definitely think he’s an issue for teams. I think this league, when it comes to third downs and things like that, you move the chains based off of matchups, which allows you to get points in the long run.”

This 41-yard Week 15 reception against the Cincinnati Bengals is a perfect example of how McKinnon (No. 21) can take advantage of schemed matchups and provide yards after the catch to create explosive receptions out of the backfield, doing more than a traditional running back.

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At the snap, the two Vikings receivers to the right side take the two Bengals defenders inside on a flood concept, with cornerback Darqueze Dennard (No. 21) passing his coverage off to the linebackers as receiver Laquon Treadwell (No. 11) runs a drag route underneath.

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However, Dennard’s hesitation toward Treadwell inside is all McKinnon needs to get outside into free space and catch the ball in position to move upfield.

Treadwell and receiver Stefon Diggs are running a mesh concept underneath—essentially crossing drag routes—and Diggs’ presence on the formation’s right side takes linebacker Hardy Nickerson (No. 56) away from McKinnon, giving him even more free space.

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McKinnon is then able to turn Dennard and safety Clayton Fejedelem (No. 42) around as he pivots inside to gain more yardage, and his value as a schemed receiver becomes apparent.

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Last year with halfbacks Carlos Hyde and Matt Breida, and fullback Kyle Juszczyk, Shanahan had a reasonably talented backfield. But he didn’t have anyone with the ability to turn intelligent schemes into game-changing plays. With Freeman and Coleman in Atlanta the year before, Shanahan made things happen differently because he had two running backs capable of winning as receivers.

McKinnon didn’t do that in Minnesota, but you can see the potential for it in this 27-yard touchdown reception against the Green Bay Packers in Week 6.

Pre-snap, receiver Adam Thielen (No. 19) motions from left to right to reveal Green Bay’s man coverage.

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The Packers are also running a cross blitz, crossing linebackers Jake Ryan (No. 47) and Blake Martinez (No. 50) to pressure quarterback Case Keenum (No. 7). Keenum doesn’t have a ton of time, so McKinnon, who delayed his movement to the blitz to sell his role as a potential blocker, releases quickly upfield.

This would be two defenders on one blocker, and the blitzers are getting a free release, so the best thing for McKinnon is to get into open space and take the quick pass.

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Once he gets that, McKinnon outruns linebackers Clay Matthews (No. 52) and Nick Perry (No. 53). With center Pat Elflein (No. 65) and guard Jeremiah Sirles (No. 75) blocking upfield, he has a clear path to the end zone.

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As was the case with the big play against the Bengals, McKinnon’s electric speed in space makes all the difference. If you extrapolate his position at the catch to a slot receiver role, you see how Shanahan might use him outside the backfield.

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The coach made it clear in that press conference he’ll use McKinnon in new ways, saying the back’s tape didn’t match his stats.

“I’m not going to get into all the whys, but I know the stuff we liked him on—if I could just cut up those numbers I think they would have been good numbers,” Shanahan said. “But when you take the whole accumulation of things, I think they watered things down.”

That’s quite a thing to say about an opposing coaching staff, but Shanahan has the track record to back it up.

Of course, if McKinnon is to be the 49ers’ starting running back, he’ll have to create big rushing plays. At 5’9″, 205 pounds, he doesn’t show the consistent in-line power to break contact and be creative between the tackles. But he has exceptional vision behind the line of scrimmage, and he can sniff out gaps and use his elusiveness to quickly get to the second level.

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This 58-yard Week 5 touchdown run against the Chicago Bears shows how well McKinnon paces himself behind his blockers. He then turns on the jets for another big play.

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The Vikings run a tremendous slide to the right, with Thielen (No. 19) drag-blocking linebacker Leonard Floyd (No. 94), receiver Michael Floyd (No. 18) putting a credible seal block on linebacker Christian Jones (No. 52), left guard Nick Easton (No. 62) cutting linebacker Jonathan Anderson (No. 58) and Elflein (No. 65) crossing to block cornerback Kyle Fuller (No. 23).

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There’s a lot going on, and this is as good of a series of coordinated blocks as you will see, but it’s also up to McKinnon to wait until everything’s open to blast through. This combination of patience and acceleration is common among the league’s best backs. Safety Eddie Jackson (No. 39) is the last line of resistance, and McKinnon easily jukes him.

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Shanahan probably envisions a primary backfield featuring McKinnon and Juszczyk in I formation settings, with McKinnon as the moveable chess piece. Juszczyk can do more than block—he also has the potential to get free in space for the occasional pass play, as he did against the Jacksonville Jaguars in a Week 16 44-33 win.

Linebacker Paul Posluszny (No. 51) can’t keep up, as seen below, which brings us back to Shanahan’s dominant schematic conceit with his running backs: to target the weakest linebacker in coverage until the opposing team is forced to take that player off the field.

Still, based on the money and intent, it’s clear McKinnon is 49ers’ primary running back, and he’s even happier than his coach about it.

“Ever since I’ve been in the league, I’ve been a third-down back,” McKinnon said, per Keiana Martin of the team’s official site. “That’s the tag that’s been placed on me. I’m ready to exceed those expectations.”

He’s in the right place. In Shanahan’s system, a third-down back is an every-down back, because he’ll be moved around frequently to maximize his abilities and stress defenses. The combination of coach and player in this case could produce the NFL’s next primary offensive weapon.