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Not every running back is created the same. Some are squatty backs with inherent power and contact balance without much speed. Some are small, dynamic athletes who can hit home runs. Others aren't overly fast but are ultra-bouncy, making them nearly impossible to bring to the turf. 

To provide a unique view of the running back position in the 2021 draft class through this lens, I've divided the class as a whole by type. Below, we'll take a look at seven different groupings (also check out our look at the quarterback and wide receiver positions).

Bouncy backs with big-time elusiveness and contact balance

Najee Harris, Alabama
Javonte Williams, North Carolina
Khalil Herbert, Virginia Tech
Jaret Patterson, Buffalo
Kylin Hill, Mississippi State

At 6-foot-1 and 230-ish pounds, Harris is remarkably elusive, the possessor of some of the most explosive cuts in the entire class. And, of course, he's a bull to bring to the turf because of his super-thick lower half and natural power. Williams could be placed into a bunch of different categories because he shifts running styles based on the run play or the look from the defense. He's extremely well-rounded, capable of bull-dozing runs, quick slashes to the cutback lane on a zone run or simply sinking his hips and jump cutting a linebacker in the hole. Tacklers ricochet off him. 

Herbert relies on his bounce more than any back in the class, and he's amazingly balanced through contact because it's so difficult for a defender to square him up thanks to his elite wiggle. Maybe the most underrated runner in this draft. 

As for Patterson, he's built like a fire hydrant and can piece together two or three cuts in one run to leave an entire defense wondering if it's actually possible to tackle him. Hill too is a contact-balance specialist with serious twitch after getting the handoff and when a defender forces him to change directions.   

One-cut slashers who win with burst more than elusiveness

Travis Etienne, Clemson
Rakeem Boyd, Arkansas
Justin Henderson, Louisiana Tech
Jermar Jefferson, Oregon State

Etienne is the ultimate "slasher" in this class. Get him on a stretch play or well-blocked power run, he'll make one 45-degree cut then be gone. And his home-run hitting ability is special. He won't bounce around and jump cut three times before exploding down the field. He's an efficient North-South runner with good contact balance who wins with electric acceleration and long speed. 

Much of the same can be said about Boyd, but all at a lesser degree of course. Henderson is my favorite Day 3 back -- and don't be shocked when he's not drafted. He's built low to the ground and gets downhill has as well as any back in the class. Plus, he has just enough athletic ability to make a tiny cut to avoid a big hit and sneak through a tiny lane. 

Jefferson has outstanding vision and is going to get exactly what is blocked for him on every run. Get him in a zone system and watch him flourish. It wouldn't surprise me if Kyle Shanahan picks him on Day 3. There's some long speed to his game too. 

Big backs with impressive quicks, contact balance and limited juice

Trey Sermon, Ohio State
Rhamondre Stevenson, Oklahoma
Gerrid Doaks, Cincinnati

B.J. Emmons, Florida Atlantic
Trey Ragas, Louisiana

Sermon is easily my RB4 in this class, because of his complete game at 6-0 and 215 pounds. His movement talent creates the illusion he's much smaller, then you catch him lowering the boom through the second level and realize every defensive back trying to tackle him comes up empty. 

While his burst isn't nearly as impressive, Stevenson is your classic boulder of a back with good feet to skirt contact behind or close to the line of scrimmage, and old-school power through tackles. Speaking of old-school power, Doaks is just shy of 6-0 but measured in close to 230 pounds at his Pro Day, and he plays precisely how you would expect for a runner of his stocky stature. 

Emmons is another runner with a thick midsection and lower half who moves like he's much lighter. Downfield juice isn't really there with his game but for a powerful runner, he possesses decent slipperiness early in runs. Ragas is one of the stiffest backs in the class, with fullback-like acceleration and fullback-like power. 

Hybrid scat back/slot receivers who'll thrive in the screen game 

Kenneth Gainwell, Memphis
Demetric Felton, UCLA
Michael Carter, North Carolina

Gainwell and Felton have freaky running-back-playing-receiver reps on film, and those high-level plays running routes and tracking the football down the field will be big reasons why they're picked somewhere in the middle of the draft, and both could land on Day 2. 

They're small-framed, adequate runners with some juice and bounce through running lanes. Their legitimate hybrid abilities will make him more valuable than where they're ultimately picked. Both could align in the slot and win against some NFL nickel corners early in their careers. 

Carter is more of a screen-game monster than a back with slot wideout potential, but his game features so much burst and outstanding vision, it wouldn't be foolish to get him some reps split out at receiver once he's in the NFL.  

Speedy gadget types with good/great quickness

Javian Hawkins, Louisville
Chuba Hubbard, Oklahoma State
Elijah Mitchell, Louisiana 
Pooka Williams, Kansas

If you're looking for low-volume, high-impact types at the running back spot in this class, first look to Hawkins from Louisville. He's little, yet twitchy and obliterates pursuit angles down the field with his long speed. He ran a 4.44 40 at his pro day. I think he's faster than that on the field. 

Hubbard didn't break off as many big-gainers in 2020. But he absolutely can leave defenders in the dust, and he's not the easiest to tackle despite having a smaller, more slender frame. Mitchell was the speed-based back in Louisiana's backfield and there's some thickness in his lower half. 

Williams is electric in space and has serious downfield jets in a small frame. Get him -- and everyone in this group -- on jet sweeps, tunnel screens etc. 

Sleeper I couldn't leave off this article

Kene Ngwangu, Iowa State

Ngwangu carried the ball a minuscule 143 times in four seasons at Iowa State. The efficiency popped though, as he finished his career with a 5.2 yards-per-carry average. Over his final two campaigns in Ames, Ngwangu accumulated 454 yards on just 77 carries, which equates to a bulky 5.9 yards-per-pop average. 

He has a chiseled, low-center-of-gravity frame with high-level twitch and serious downfield speed. As the primary returner for Iowa State, Ngwangu averaged nearly 27 yards per kick return in his four years in that full-time role. He's a special athlete who could be the Antonio Gibson of this draft class.