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A big rapper says Coachella's to blame for an unprovoked attack by the music festival's security that left him with with some serious and lifelong injuries ... thus, a new lawsuit.

Belly just filed against the famous festival, claiming it caused the incident by hiring a security company that WAILED on him back in April 2018 while Belly's friend, The Weeknd, performed on the main stage. According to new legal docs obtained by TMZ ... Belly claims approximately 25 security guards pummeled him without cause.

Play video content 4/20/18 TMZ.com

Belly -- who performed at the festival earlier that night -- says he had all the necessary credentials to access all areas on the grounds ... including the most exclusive and restricted VIP sections.

Belly -- who enlisted the firebrand of attorney Ben Meiselas -- says he was headed to a backstage VIP area, when out of nowhere, security bum rushed him and repeatedly grabbed, punched, kicked and choked him. The brutal attack was all caught on video.

Belly says the attack left him bruised, battered, concussed and nearly unconscious. He claims he suffered permanent physical and mental pain and trauma. Belly -- who is also suing Coachella's organizers and the security firm it hired -- wants a ton of money, but he wasn't specific.