Adrian Peterson has been suspended without pay for at least the remainder of this season.
The NFL announced its highly anticipated ruling Tuesday morning, stating that the Minnesota Vikings' star running back will not be considered for reinstatement before April 15, 2015, for violating the league's personal conduct policy.
The league said it informed Peterson of the ruling in a letter from commissioner Roger Goodell, who spelled out a path for his return to the field.
The Vikings have six games left this season. The league's enhanced disciplinary policy calls for a six-game suspension for first offenses of assault, battery or domestic violence. Aggravating circumstances warrant higher levels of discipline, and Goodell's letter to Peterson spelled that out.
But a league source told ESPN's Ed Werder that it is "very possible" that Peterson could return to the field for this Sunday's game against the Green Bay Packers, pending a ruling by the independent arbitrator in Monday's grievance hearing.
The NFL Players Association quickly announced its plan to appeal and sharply rebuked what it calls the league's inconsistency and unfairness in the process.
If arbitrator Shyam Das rules in favor of Peterson, he could play while his appeal of Tuesday's suspension is heard, according to rules laid out in the NFL's collective bargaining agreement. Goodell, under the CBA, would decide who hears Peterson's appeal.
Another source told ESPN's Chris Mortensen that if Das decides Peterson should be reinstated, the issue will become more complex and "there will be many lawyers involved."
Peterson was indicted in September on a felony charge of injury to a child for using a wooden switch to discipline his 4-year-old son earlier this year. The All-Pro pleaded no contest to a lesser charge of misdemeanor reckless assault Nov. 4, setting the stage for the NFL's ruling.
Peterson was placed on a special exempt list at the sole discretion of Goodell on Sept. 18, essentially paid leave while his case went through the legal system.
The NFLPA said Peterson was told that would count as time served for any suspension levied, citing an unnamed NFL executive. League spokesman Brian McCarthy told The Associated Press in an email that Peterson's stay on the exempt list was taken into account.
"There were aggravating circumstances that led to the discipline announced," McCarthy told the AP.
The league's statement included excerpts of the letter written by Goodell, who has required that Peterson undergo counseling and treatment in order to be reinstated.
"We are prepared to put in place a program that can help you to succeed, but no program can succeed without your genuine and continuing engagement," Goodell wrote in the letter. "You must commit yourself to your counseling and rehabilitative effort, properly care for your children, and have no further violations of law or league policy."
The Vikings also released a statement, saying they "respect the league's decision and will have no further comment at this time."
Peterson's case revived a debate about corporal punishment, which is on the decline in the U.S. but still widely practiced in homes and schools. Peterson has repeatedly claimed that he never intended to harm his son and was disciplining him in the same way he had been as a child growing up in East Texas.
Goodell, however, expressed concern in his letter that Peterson does not "fully appreciate the seriousness" of his conduct.
"You have shown no meaningful remorse for your conduct," Goodell's letter said. "When indicted, you acknowledged what you did but said that you would not 'eliminate whooping my kids' and defended your conduct in numerous published text messages to the child's mother. You also said that you felt 'very confident with my actions because I know my intent.'
"These comments raise the serious concern that you do not fully appreciate the seriousness of your conduct, or even worse, that you may feel free to engage in similar conduct in the future."
The boy suffered cuts, marks and bruising to his thighs, back and on one of his testicles, according to court records. Goodell cited those injuries in his letter to Peterson.
"The difference in size and strength between you and the child is significant, and your actions clearly caused physical injury to the child," Goodell's letter said. "While an adult may have a number of options when confronted with abuse -- to flee, to fight back, or to seek help from law enforcement -- none of those options is realistically available to a four-year-old child.
"Further, the injury inflicted on your son includes the emotional and psychological trauma to a young child who suffers criminal physical abuse at the hands of his father."
The NFL stated that Peterson and the union did not provide the league with information that "would be relevant to evaluating Peterson's conduct." The league also claimed that Peterson, his representatives and the union would not participate in a disciplinary hearing that had been scheduled for last week.
The union responded with its statement, which cited a "credibility gap" within the NFL's disciplinary process.
"The decision by the NFL to suspend Adrian Peterson is another example of the credibility gap that exists between the agreements they make and the actions they take," the NFLPA statement said. "Since Adrian's legal matter was adjudicated, the NFL has ignored their obligations and attempted to impose a new and arbitrary disciplinary proceeding.
"The facts are that Adrian has asked for a meeting with Roger Goodell, the discipline imposed is inconsistent and an NFL executive told Adrian that his time on the commissioner's list would be considered as time served. The NFLPA will appeal this suspension and will demand that a neutral arbitrator oversee the appeal. We call on the NFL Management Council to show our players and our sponsors leadership by committing to collective bargaining so a fair personal conduct policy can be implemented as quickly as possible."
NFLPA executive director DeMaurice Smith echoed those sentiments during an interview Tuesday on ESPN Radio's "Mike & Mike," accusing the NFL of "making it up as they go along."
"Our initial reaction is that the process that the NFL has employed since the beginning of the season has been arbitrary, inconsistent and uneven," Smith said. "You get the feeling that the NFL, over the past few months, has been simply making it up as they go along. That is something that is not in the best interest of the game, the players, or the sponsors."
Peterson received support from Vikings teammate Jerome Felton, both on Twitter and in comments to ESPN's Josina Anderson. Felton said this issue goes beyond Peterson and should concern all NFL players.
"The players need to stand together," the fullback told ESPN. "[Suspensions] can't just be some arbitrary number that they come up with. There needs to be a set policy, and it's something that is followed, and it needs to be collectively bargained. If it's not, then there are always going to be issues. There will always be fighting and there will always be lawyers."
Goodell announced Aug. 28 that the league would toughen punishment for players involved with domestic violence. That action stemmed from a torrent of criticism for the initial leniency toward former Ravens running back Ray Rice following a caught-on-camera knockout punch of the woman who is now his wife.
ESPN's Ed Werder, Chris Mortensen, Josina Anderson, Adam Schefter, Ben Goessling and The Associated Press contributed to this report.