Douglas F. "Doug" O'Neill (May 24, 1968) is an American Thoroughbred horse trainer. He was born in Dearborn, Michigan, and resides in California, where he trained the 2012 Kentucky Derby and Preakness Stakes winner, I'll Have Another. O'Neill and his family reside in Santa Monica, California.
In 1986 he began working in Thoroughbred horse racing as a stable hand and eventually a training assistant. In 1994 he obtained his professional trainer's license and since the early 2000s has been a major figure on the California racing scene, with the largest stable in Southern California and one of the largest and most successful in the United States. He gained national attention for his Breeders' Cup wins and international recognition for winning the 2003 Japan Cup Dirt at Tokyo Racecourse.
Canadian owned I'll Have Another, trained by O'Neill, won the 2012 Kentucky Derby on May 5, 2012. The horse also won the 2012 Preakness Stakes and was viewed as a potential Triple Crown winner. However, in the meantime, O'Neill's multiple violations of medication rules caught up with him and he was given a 45-day suspension, though because O'Neill's suspension was not set to begin prior to July 1, 2012, he was permitted to run I'll Have Another in the 2012 Belmont Stakes.
The race featured tightened security, including a "dentention barn" where all entrants had to be stabled together in a specially-designated barn, starting three days before the race. Although dubbed the "O'Neill Rules" by the New York Post, the potential for a triple crown also increased the scrutiny given the race. Furthermore, the New York Racing Association had also been taken over by the state of New York earlier in the year due to problems with horse deaths and questions surrounding "exotic bets."
O'Neill scratched I'll Have Another from the Belmont the day prior to the race, citing a tendon injury. The decision to scratch I'll Have Another was based on the O'Neill's monitoring of swelling in the horse's foreleg early in the week of the Belmont, and confirmation by Dr. James Hunt, a NY-based veterinarian that the horse risked further injury if he ran. Racing fans and some commentators speculated that O'Neill scratched I'll Have Another not because of a relatively minor tendon injury, but because he "couldn't doctor the horse the way he needed to because of the detention barn." Others dismissed this as a conspiracy theory. John Sabini, chairman of the New York State Racing and Wagering Board stated that the decision to scratch the horse was disappointing but that the trainer and owner "put the welfare of the horse first, showing true horsemanship." 
In May 2012, after a two-year legal battle, the California Horse Racing Board (CHRB) found that O'Neill was responsible for a horse that tested with excess carbon dioxide levels above the permitted level of TCO2. As a result, though he was not found guilty of "milkshaking" the horse - providing an "illegal performance-enhancing mixture," O'Neill was deemed responsible for the animal's care, barred from horse racing for 45 days and fined $15,000.
A few days after I'll Have Another won the 2012 Derby, New York Times writers Joe Drape and Walt Bogdanich ran a story discussing O'Neill's extensive history of medication violations. It ran on the front page of the paper. Additional criticism came from other quarters, including Frank Deford of NPR, who expressed his view that both O'Neill and the owner of I'll Have Another did not deserve to win the Belmont, describing O'Neill as "a charming enough character, but a drug cheat nonetheless." Due to the reports of multiple medication violations, O'Neill had been nicknamed "'Drug' O'Neill." However, some industry experts, such as Andrew Beyer of the Washington Post, felt that O'Neill was a skilled trainer who had made some mistakes but had been "maligned." Taking a middle ground, Bill Dwyre of the Los Angeles Times viewed O'Neill's violations as a "misdemeanor." Bogdanich found that O'Neill had 15 medication drug violations during his career and had "milkshaked" horses—an illegal treatment for fatigue that involves inserting a tube down a horse's esophagus to administer a mixture of substances. In a 2012 interview with NPR, Bogdanich criticized a lack of enforcement of drug rules in American horse racing, noting that although O'Neill faced a 180-day suspension for milkshaking, any punishment imposed upon him have would little impact on his livelihood: "He could turn it over to his assistants, his stable, and never miss a beat. The horses keep running. If they win, they keep getting their purses. You know, that's what America lacks that the rest of the world has. They have law and order." In October 2012, the Los Angeles Times ran a story on O'Neill's gregariousness and kindness to others, suggesting that jealousy motivated his detractors.
In October 2014, O'Neill was given another 45-day suspension as a result of a June 2013 violation at Belmont Park. By this time, O'Neill had accumulated 19 drug violations. The New York Racing Association also fined him $10,000. However, as happened in 2012, they agreed that he would not have to serve his suspension until after a major race, this time the 2014 Breeders' Cup. He was also given an additional 45-day suspended sentence, which would "be served if he incurs another medication violation before December 18, 2015, at any US track." Following his New York suspension, he was given a separate 45 day suspension in California, based on his violation of the CHRB restrictions from 2012 due to the 2013 New York violation. This suspension foreclosed his ability to train horses for the 2014 Breeders' Cup. In addition, California gave him an 18-month probation period on top of the 45 day ban, during which time he cannot have any further Class I, II, or III drug violations in any part of the USA or internationally. While his previous penalties were based upon the dates that assorted complaints were filed or adjudicated, this time the ruling was that the "deciding event" for any violation would be the date when the offense actually occurred. His assistant trainer was put in charge of conditioning horses for his stable, and one horse was transferred to a different trainer.
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