Redskins running back Robert Kelley, right, during Washington’s first preseason game. (Brynn Anderson/Associated Press)

Redskins running back Robert Kelley was a guest on ESPN 980’s “Inside the Locker Room” on Tuesday and, not surprisingly, the first question for the undrafted rookie out of Tulane was about the nickname that Redskins Coach Jay Gruden revealed to the world last week.

“Rob did a good job,” Gruden said of Kelley’s preseason debut against the Falcons.  “‘Fat Rob,’ that’s what is on his backpack. He did a nice job. … That’s his nickname in college if you didn’t know that – ‘Fat Rob’ Kelley. But anyway, he was impressive. He’s been impressive since we got him.”

Kelley’s simple explanation for how he got the nickname is about what you might expect.

“My senior year, my running backs coach brought me a backpack with ‘Fat Rob’ [inscribed on it], a nickname I actually earned in the offseason eating a lot of food,” Kelley said this week. “I don’t like to talk about it.”

The man responsible for giving Kelley the nickname — and the customized backpack — was happy to talk about it, and offered a slightly different take on the moniker’s origin.

“That’s what I would call him, ‘Fat Rob,'” former Tulane running backs coach David Johnson, who left New Orleans to join new Memphis Coach Mike Norvell’s staff in December, said Friday. “It had nothing to do with his weight, it was really about his heart. I would call him ‘Fat Rob’ all the time because his heart was so big.”

Okay, but the 20-plus pounds Kelley put on during his senior season weren’t all concentrated in his aorta, right?

“He did gain a little bit of weight his senior year because he wasn’t practicing during the spring, but he had a really big heart and sometimes he was loyal to a fault,” Johnson said. “For me it was more about his heart and his character. It kind of came a little true when he gained that weight.”

Kelley starred at O. Perry Walker High in New Orleans and was Tulane’s leading rusher as a sophomore in 2012. He was declared academically ineligible to participate in the spring 2014 and sat out the entire 2014 season. Kelley eventually earned his degree and returned to the team as a fifth-year senior last season, when he rushed for 232 yards on 65 carries. After the final game of his college career, Kelley said he weighed 249 pounds. By Tulane’s Pro Day in March, he was down to 225 pounds and called Johnson to let him know that he performed well in front of scouts.

“He said, ‘Coach, coach, I ran a good time and I kept running the ball hard,'” Johnson recalled. “He was so proud of himself and I was proud of him. It was really tough for him. Eighty or 90 percent of people would’ve quit if they were in his position. He didn’t have a stellar senior year, but even though he was the third-string running back on the depth chart, he was always the leader of that room.”

Kelley went undrafted, but signed with the Redskins as a free agent in April and rushed for 40 yards and a touchdown in his preseason debut. With Matt Jones and Chris Thompson out for Friday’s game against the Bills, Kelley — listed at 228 pounds — is expected to split carries with seventh-round pick Keith Marshall. Johnson, who texts and talks with Kelley often, isn’t surprised his former pupil is making a serious push to be the Redskins’ third running back.

“I know what type of kid he is, I know his athletic ability,” Johnson said. “He’s one of the most athletic people I know and I knew he would make the most of his opportunity. He came from a pro-style offense, but the biggest advantage he has is he knows protection. That’s one of the things that we kind of stressed. A lot of guys can run and catch, but can you block and can you protect that million dollar quarterback? ”

Johnson said he’ll cry if “Fat Rob” is on the Redskins’ sideline come Week 1 and could only laugh when Kelley contacted him recently to let him know that Gruden had outed his nickname.

“I told him, hey, you need a marker there,” Johnson said. “Everyone has a brand.”