Give the guy some punishment, misdemeanor assault, a couple weeks suspension...and get the teams to do something about the obnoxious fans.
Dear B Knotts,
Where I live, if you take a swing at a guy and break his nose, and you have no legal justification, you'll be charged with a misdemeanor or felony. First offense will get a probation before judgment (if you keep your record clean for a set period of time afterwards - say, a year or two - your record will be expunged).
If you use a physical object in the assault, and cause signficant injury, count on a felony charge, and likely a little time in the county lock-up.