The Redskins need “Fat Rob” to rescue them.

The backfield belongs in a triage unit. Starter Matt Jones is hurt. So are third-down specialist Chris Thompson and seventh-round pick Keith Marshall. Undrafted rookie Robert Kelley, who got his weighty nickname at Tulane, is still standing.

Kelley first caught coach Jay Gruden’s attention in rookie minicamp. At 6 feet and 228 pounds, he is a strong, straight-ahead runner. That weight is light for Kelley, who has said he weighed 249 after he finished his college career.

Kelley started for Washington on Friday against Buffalo, picking up 51 yards on 12 attempts. When Marshall suffered a sprained elbow on his first carry, Kelley continued to thrive and even picked up a blitz to protect Kirk Cousins.

Jones and Thompson could be back for the season opener, while Marshall is expected to miss at least three weeks.

Gruden needs to decide now who will be his primary back. The team seems settled on Jones, but it should be Kelley, who has led the team with 99 yards rushing in the preseason.

Really, what has Jones done after a mediocre rookie year? He’s rushed for 32 yards on nine carries this preseason and sprained an AC joint in his left shoulder in the second game against the Jets. The injury shouldn’t keep Jones off the field, but he’ll likely have to play through pain. Jones could best contribute as a spot player.

The Redskins ran the ball a meager 44 percent of the time last season and could run even less this year with a loaded passing attack, but building continuity in the backfield would be helpful.

If Kelley proves in the opening weeks he can handle the load, then he should be the top ball carrier.

With three other rushers injured, Kelley’s teammates have shown confidence in him.

“I think when you’re a rookie and undrafted … what you need is belief,” Cousins said. “You need people around you who believe in you and have confidence in you, because he does have the talent and he can run the football well.”

Tackle Trent Williams was impressed with Kelley’s effort against the Bills.

“[Kelley] found the creases, he moved forward,” Williams said. “Obviously, there are some things we can clean up, but I think it was a good outing for him.”

Gruden sees Kelley as an overlooked gem he can develop. The coach was facing a tough decision between potentially keeping Kelley or Marshall, but Marshall’s elbow sprain has tabled that discussion for now. Kelley has quickly risen from borderline reserve to interim starter.

“I feel confident that I gave myself a better opportunity to make the roster,” Kelley said.

The Redskins need a healthy power runner, not a banged-up back.

At this point, Kelley stands alone.

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