MMA Star Josh Neer -- Case Closed in Gym Beatdown ... 'No Rules Were Broken'

MMA fighter Josh Neer's gym beatdown was NOT a violation of Iowa Athletic Commission rules ... and therefore he will not be disciplined for his role in the fight ... TMZ Sports has learned.

As we previously reported ... the IAC launched an investigation into Neer (who's 36-14 in pro fights) to see if he broke any Commission rules when he decided to fight Patrick Martin earlier this week.

But according to IAC honcho Joe Walsh ... Neer is clean -- telling TMZ Sports, "We've determined that we don't have anything in our rules that covers incidents that take place in a gym."

Walsh adds, "Because of that, there will be no further investigation. We've closed the case."