Joel Rosario, the leading rider at Del Mar, has had a complaint filed against him by the California Horse Racing Board alleging he "did not put forward his best effort riding his horse to the finish line" in the final race at Del Mar on Sept. 6.\nA hearing, originally scheduled for Wednesday at Fairplex Park, has been postponed until Oct. 2 at Santa Anita, Rosario's agent, Vic Stauffer, said Saturday.\nRacing is currently being conducted at Fairplex Park, which fills the gap between Del Mar, which closed on Sept. 9, and the Oak Tree meeting at Santa Anita, which opens Sept. 30. Rosario is not riding at Fairplex.\nRosario was aboard Cedros in the 11th race on Sept. 6, a maiden race at 1 1/16 miles on turf. Cedros, a 4-1 shot in the field of 10, battled outside another rival for the early lead through the first half-mile of the race, then, according to the race's official chart, "fell back some leaving the second turn and angled in, continued along the rail in the stretch and was edged for the show." He finished a head behind the third-place finisher, Never.\nCedros is trained by John Glenney and is owned by Glenney and his wife, Kim.\nAccording to Glenney, he complained to Del Mar's stewards about Rosario and Stauffer after Stauffer approached Glenney the morning after the race and asked if Cedros was for sale.\n"I thought that was highly unusual," Glenney said in a telephone interview from Kentucky, where he returned after Del Mar's season ended. "I had asked Rosario to make sure he kept Cedros outside horses. It wasn't a good ride. And then to get the offer the next morning? I've never heard of something like that before. I asked the stewards to look into it. If they saw something, and decided to pursue it, so be it."\nThe complaint filed against Rosario cited him for violations of three racing board rules. One pertains to unsatisfactory rides - "no jockey shall take his horse back without reasonable cause . . . or otherwise ride in a manner which is inconsistent with using the best efforts of the horse he is riding," the rule states in part - and another is titled "conduct detrimental to horse racing."\nNo charges have been filed against Stauffer. Mike Marten, the spokesman for the racing board, could not say if Stauffer was even being investigated. "The CHRB doesn't confirm or deny investigations of this sort," he said.\nStauffer on Saturday said, "Both Joel and I will not say anything until after the hearing."\nIn addition to being the leading rider at Del Mar this summer, Rosario topped the standings at the Hollywood Park meeting earlier this year.