The 33-year-old—who was reportedly there to support his students—was caught on video during a scuffle that featured several men throwing punches across seats and tables at the Hyatt hotel event.
No arrests were made following the incident.
This is the second fight involving Diaz in the past two months outside the Octagon.
According to TMZ Sports, he got into an altercation with fellow MMA fighter Tyler Diamond in May at Combate Americas, which also took place in Sacramento. Diaz reportedly slapped Diamond in the face but didn't face charges after the incident.
The lightweight is ranked No. 8 in his division but hasn't competed since losing to Conor McGregor in August of 2016. He had beaten McGregor in his previous bout.