Suffolk County Police say a driver-less Army Humvee apparently slipped out of gear and rolled down a hill, pinning a woman between the vehicle and a food trailer.
The accident happened around 5 p.m. Saturday at the 'Long Island Bacon Bash' in Farmingville.
46-year-old Suzette Lamonica was rushed to Stony Brook University Hospital where she is being treated for serious arm and leg injuries.
Eyewitnesses say it was chaos.
"Everyone was running and screaming," said Jessica Hansen.
Three other people were hurt. The Humvee was impounded for a safety check.