A US judge has overturned a four-game suspension against National Football League (NFL) quarterback Tom Brady, calling the league's disciplinary process "fundamentally unfair".
The NFL imposed the punishment following the "Deflategate" scandal.
NFL officials found that Mr Brady had colluded with New England Patriots team members to deflate footballs below the allowable limit during a playoff game.
Mr Brady can now play on 10 September against the Pittsburgh Steelers.
U.S. District Judge Richard M. Berman found that NFL Commissioner Roger Goodell's penalty suffered from "several significant legal deficiencies" including failing to notify Mr Brady about the possibility of a punishment against him.
"The court finds that Brady had no notice that he could receive a four-game suspension for general awareness of ball deflation," Judge Berman wrote.
Commissioner Goodell's inquiry concluded that Mr Brady "knew about, approved of, consented to, and provided inducements and rewards" to ensure that game balls were deflated.
Deflated footballs are considered easier to throw and catch.
In an appeal hearing last June Mr Brady admitted to NFL investigators that he had destroying his mobile phone, but claimed it was to preserve his family's privacy.
Commissioner Roger Goodell said in a statement that the league will appeal the judge's ruling.
"The commissioner's responsibility to secure the competitive fairness of our game is a paramount principle.... While the legal phase of this process continues, we look forward to focusing on football and the opening of the regular season."
Experts say Thursday's ruling is unlikely to put an end to the controversy, which has dominated sports headlines in recent months.
On Twitter, football fans are using the term "Teflon Tom," referring to a non-stick coating used on cooking pans, to either support or disparage Mr Brady.
"No one likes a cheater. Terrible message it sends to the youth and adults when obstruction of justice goes unpunished," one message on Twitter read.
ESPN sports reporter Steve Levy tweeted that while in a Boston hospital, he heard an announcement over the loudspeaker saying that "Tom Brady is free".