Puka Nacua's brother is in trouble with the United Football League -- Samson Nacua was just suspended for slapping a fan in a heated post-game altercation.
The UFL handed down the punishment on Tuesday ... stating the Michigan Panthers receiver was banned one game without pay for "an altercation with a spectator" after the matchup against the St. Louis Battlehawks at The Dome at America's Center on Saturday.
On top of the forced sit-out, the league says Nacua has agreed to do community service at some point later in the season.