Wertheimer Farm's Halfbridled, the champion 2-year-old filly of 2003, has been retired due to the recurrence of an injury the daughter of Unbridled sustained last spring.Trainer Richard Mandella said Halfbridled was galloping and preparing to undergo serious training as part of her comeback when it was detected that the filly still suffered from a cannon bone injury that had sidelined her earlier this year. "The problem she had in the spring started coming back, so we decided to retire her," Mandella said.Halfbridled retired with four wins and two seconds from six starts and earnings of $959,400. Included among her victories were the Breeders' Cup Juvenile Fillies (gr. I), Del Mat Debutante (gr. I), and the Oak Leaf Stakes (gr. I), all during her championship season. This year, the filly finished second in the Santa Anita Oaks (gr. I) and Stonerside Beaumont Stakes (gr. II).Halfbridled was sent to Haygard Farm in Paris, Ky., with the mating for 2005 yet to be determined.