The crowd began throwing rocks and bottles.
By 2 a.m. Friday, six people were in custody. Three of the arrested were from the actual fight and three were from the mob.
It's not clear what started the disturbance.
One person from the fight was hospitalized. No deputies were injured.
The Key Club issued an apology on Friday, stating: "Key Club would like to sincerely apologize to the city of West Hollywood and our incredibly loyal fan-base for the unfortunate events that occurred last night. We work hard every day to provide a safe and enjoyable concert experience for all of our patrons. We hope that you will continue to trust and support us in the future."
