The rider, 40-year-old Leonel Trejo of New Castle, fell around 9:30 p.m. during a performance at the NUR Temple in the 100 block of S. DuPont Highway.
Police say Trejo, an experienced bull rider, fell after about a minute into the ride.
That's when the bull stepped on Trejo's chest area. He was not wearing protective equipment, police said.
Trejo was rushed to Christiana Hospital where he was pronounced dead.
An autopsy will be performed to determine an exact cause of death.
Police say an investigation into this accident continues.