NBA YoungBoy Fan Pulverizes Elderly Man During Kansas City Concert

NBA YoungBoy has some rabid fans ... but one took it all too far when he went totally ballistic and beat the living piss out of an elderly man working the rapper's concert in Kansas City last weekend.

Video posted on X captured every moment of Sunday's beatdown in the crowd inside KC's T-Mobile Center during NBA's sold-out "MASA" Tour.

Check out the clip ... the young fan -- who police describe as a juvenile -- slams the guest services employee into the seats and starts using his face as a punching bag. During the brutal attack, the old man's glasses are knocked to the ground.

Another person jumps in and grabs hold of the assailant, pulling him off the victim, who reportedly suffered serious injuries that were not life-threatening.

Police are now involved. A rep for the KC Police Department tells TMZ Hip Hop ... "A juvenile male was detained and subsequently released to his guardian pending further investigation." The rep also said detectives are "actively working with prosecutors for consideration of applicable charges."

Ironically, Kansas City's mayoral office lauded NBA YoungBoy for his "Stop The Violence" movements on Sunday but as you can see, his live show was anything but that.