Beulah Park racetrack near Grove City, Ohio, cancelled its Thursday race card out of respect for the family of apprentice jockey Josh Radosevich, who died Wednesday in an accident during the third race.Radosevich, 16, was fatally injured when his mount broke down in upper stretch, throwing the young rider to the ground. A track spokesman said Radosevich died from injuries sustained when his mount rolled over on him, but a witness said he may have been struck by a trailing horse.Radosevich was racing on the lead aboard Nyoka in the 4 1/2-furlong race for $3,500 claimers, when the gelding broke down approaching the three-sixteenths pole. Paul Heizer, who until two weeks ago was Radosevich's agent and witnessed the accident, told The Blood-Horse that one of the trailing horses may have clipped Radosevich in the head.The Equibase chart of the race said three horses -- Tradewest, Wild Dance, and Hubble the Charmer--either hit Nyoka or Radosevich. Nyoka, trained by Charles Lawson, was euthanized. Hubble the Charmer tripped over the fallen Nyoka and sent Jorge Collazo Jr. to the ground. He was treated and released at Grant Medical Center in Columbus.Heizer said Radosevich was taken to Grant Medical Center after the accident, but is believed to have died on the track. Radosevich's father, Jake Radosevich, a trainer at Beulah, rushed onto the track when his son fell, the boy's mother said."He had blood coming out of his mouth and ears and he wasn't conscious," Shelly Radosevich said of her son, a sophomore at Central Crossing High School in suburban Grove City.Radosevich, whose parents own a farm where they raise horses, had been riding since he was in the fifth grade, his mother said. He received his jockey's license about six weeks ago, she said, his first win coming at Beaulah Park on Oct. 14. He won 14 races at Beulah and five at Mountaineer Park in West Virginia. Josh Radosevich, whose grandfather Joe also trained horses, rode for his father in Wednesday's first race, finishing sixth aboard Timber King."I have known Josh since he was two, and this is the happiest I had ever seen him," said Heizer. "He really cowboyed up every time he went out there. He was really coming into himself. There are just no words to describe how bad I feel."Beulah cancelled the remainder of Wednesday's races.The Associated Press contributed to this report.