Snooki Lookalike Assaulted at Rockfest

TMZ obtained footage from Saturday's Rockfest concert in Kansas City, MO ... where Slash was performing ... when an unidentified Snook-alike took a hard boot to the face from a very angry, very large male.

Sources at the scene tell TMZ ... the man had already gotten physical with other concertgoers when the Snook-alike decided to tell him off with a few choice words.

The man -- who didn't appreciate the criticism -- responded by planting his foot right in her grill ... dropping her to the floor like a sack of potatoes ... and igniting a massive brawl involving a bunch of scary looking individuals.

Eventually, the fight was broken up ... and sources at the scene tell us the Snook-alike appeared to be OK.