NBA legend Paul Pierce is being sued over an altercation with a security guard in the stands at the Conor McGregor vs. Khabib Nurmagomedov fight ... TMZ Sports has learned.
The man behind the suit is Christopher Mostello -- who was working security at the T-Mobile Arena on Oct. 6, 2018 for UFC 229 when he got called over by a supervisor to respond to an incident involving Pierce.
Mostello claims he rushed over and was told Pierce had gotten aggressive and physical with the security supervisor -- a woman -- because she had asked for his ticket before allowing him back to his seat.