Pittsburgh Steelers linebacker James Harrison is reportedly getting fined by the NFL, but not for what you might think.

Over the weekend Harrison and dozens of other current and former NFL players reportedly participated in the Pro Football Arm Wrestling Championship at the MGM Grand Hotel & Casino in Las Vegas.

USA Today reports that a portion of the prize money for the event, which will reportedly be broadcast on CBS in May and June, will be donated to a charity of the winning players’ choice.

Harrison posted photos of the event to his Instagram account.

The NFL has now reportedly launched an investigation into whether players broke league rules which prohibit players from appearing at Casinos in a promotional capacity.

NFL Network’s Ian Rapoport reports that NFL will fine the players involved.