Peterson spent the past two years with Washington, leading the team in rushing over that time with 1,940 yards and 12 touchdowns. He has rushed for 14,216 yards, trailing Barry Sanders by 1,053 yards for fourth place on the NFL's career list. Peterson ranks fourth with 111 rushing touchdowns.
"It comes as a surprise. I didn't feel I showed anything that would warrant being released," Peterson told ESPN.
He also was adamant about wanting to continue playing.
"Oh, yeah, without a doubt," Peterson said. "I definitely want to play."
Washington, though, has a young roster it wants to grow. Peterson is 35 years old and considered a power runner. The team has four other running backs, all 27 years old or younger and all capable of helping in both the running and passing games.
Still, it was a surprising move considering Peterson had mostly worked all summer with the starters and was praised for his power runs and leadership. But the coaches often mentioned versatility. It has become even more important at this position, given the lack of proven talent and depth at tight end and wide receiver. Washington wants an element of surprise to boost its offense.
The team wants to use a lot of two-running-back sets and wants the backs to be multithreats. It drafted Antonio Gibson in the third round; he had played mostly wide receiver at Memphis, but Washington will use him as a running back who can align all over in the passing game. The team signed veteran Peyton Barber and has been pleased with how he can contribute as both a runner and pass-catcher.
Washington signed third-down back J.D. McKissic in free agency and also has Bryce Love, a fourth-round pick in 2019 who is coming back from knee surgery late in his last year at Stanford. Love has been practicing all summer, and one source said this week that, in a couple of months, Love could perhaps get back to where he was in college.
"I did not see an indicator I would be released," Peterson said. "Ultimately it came down to them knowing Bryce is coming back, and he's looking good, looking healthy. Barber is a younger guy as well who can contribute. At one point, I wouldn't have been surprised if all five of us made the team, with all of them except me being able to play special teams."
Washington also cut running back Derrius Guice this offseason. Guice was released Aug. 7, less than two hours after he was arrested on domestic violence charges in Loudoun County, Virginia. Guice also has been accused of raping two women while he was at LSU in 2016, according to a report in USA Today.
A week ago, Peterson appeared to be set for a roster spot. But in the past week, the comfort level shown by quarterback Dwayne Haskins in the team's offense, plus the improved showing of Love, lessened the need for Peterson.
Peterson said in two-back sets he still could have played the same role he always had; it just would have occurred with Gibson or McKissic having the ability to align in the backfield or elsewhere. And, Peterson said, he felt he would still be the primary back when in a one-back set.
But in the past week, he sensed a change.
"I noticed that my role would be reduced," Peterson said. "We got Gibson and J.D., and though we were all learning the same things, there are guys they selected during the draft and have in mind that they want to use for certain positions."
Washington wanted to release Peterson now to give him a better chance to sign elsewhere. Peterson said based on what he showed in training camp, he can still contribute.
"Without a doubt, I feel good about that," he said. "Maybe this could have come last week and I'd be down in Tampa Bay. That's the only thing that sucks is the season kicks off in a little over a week. But it's a good thing because teams will be making cuts and getting the roster together.
"We'll see what happens. ... Every new chapter is a blessing. Whatever comes next, I'll be blessed to attack it. I can't be down on myself. I know it wasn't because of my ability or inabilities to do something. It came down to those guys making their decision.
"It just sucks because I feel this team really has some promise and I won't be a part of it."
Washington's newcomers allow the team to use its backs in varied ways. Though Peterson could catch the ball -- with 37 receptions in two seasons with Washington -- he was viewed as a runner first and foremost, albeit one with good power. Two weeks ago, coach Ron Rivera said he could envision Peterson still running through arm tackle attempts.
"He's going to pick up four, five, six yards on second down," Rivera said. "That's what you want. That's what he's here for -- to set the tone, set the tempo for our offense as a physical team."
But with an emphasis on creativity and versatility, Peterson became expendable.
"I understand the system and what they're wanting, and I showed on film I can be effective when used as a receiver," he said. "In the one-on-one drills, I was able to show and prove I can run routes and catch the ball. And in pass protection, I was the best pass-protector we've got. That's on film as well.
"It definitely caught me by surprise. I'm in good spirits because I know those things I just mentioned. Ultimately, it came down to their preference and a new direction they were going in."
Peterson said he felt good after a red zone period earlier in the week that pitted the first-team offense against the first-team defense. On the first play, he said, he broke off a long run, untouched, for a touchdown.
"Guys were, 'oooo and aahhh,' because of a move I put on one of the cornerbacks," Peterson said. "So there's nothing I can sit here and say, physically or mentally, that I did wrong outside of them just having their preference. Me being a veteran, a Hall of Famer once I retire with the things I've done, I'm in good spirits."
Rivera said he released Peterson on Friday, ahead of the final cuts, because "Adrian deserves his day. This is a first-ballot Hall of Famer. To be treated any other way than that, I was going to struggle with that. This isn't about what he's done, but about what this group of backs has shown us, especially in the way the offense is headed. That's what this is all about. Adrian is a true pro. I was fortunate to watch the way he handles himself and the players around him. It epitomizes who he is as a player."
Rivera reached his decision Thursday night and said he woke up at 4:03 a.m. Friday thinking about how he would tell Peterson.
"It was very difficult," Rivera said of their early morning meeting. "Just because of who he is. ... He was as cool and professional as he could be."
"Anytime you move on from a person of Adrian Peterson's status, it's tough," Rivera added.
Rivera said the versatility of others helped increase what Washington could do offensively. The feeling was, with Peterson in the game, that Washington was beholden to use a style that best suited him -- but doesn't mesh with the ability to be creative.
"That played into it," Rivera said. "[But] this is not about what he didn't do. It's about what the other guys are doing for us. The guy's got football left in him."
Peterson was not in high demand when Washington signed him in the summer of 2018 after a string of running back injuries in training camp -- notably Guice's torn ACL. Peterson had dealt with injuries and a trade the previous year, rushing for a combined 529 yards with New Orleans and Arizona in 10 games.
In Washington, Peterson emerged as the team's top runner in 2018 with 1,042 yards and seven touchdowns. Then-coach Jay Gruden made him a healthy inactive in the season opener last season. Gruden felt just having a power runner limited the offense. But Peterson was active the rest of the season and finished with 898 yards for a 3-13 team.
The other running backs often praised Peterson for being what they considered an approachable legend. He was willing to share knowledge with the younger backs.
After spending 10 seasons in Minnesota, Peterson recently called Washington his "second home." He said he liked how fans embraced him.
"God willing, it'll be five more years," he said.