Nafzger trained Unbridled who won the 1990 Kentucky Derby and Breeders' Cup Classic. In 1990 he was voted the Eclipse Award for Outstanding Trainer and the Big Sport of Turfdom Award. In 1994, he wrote a book on the training of Thoroughbred horses titled Traits Of A Winner that was published by R. Meerdink Co. (ISBN 978-0929346328).
In 1998, Nafzger trained Banshee Breeze who won that year's Eclipse Award for Outstanding 3-Year-Old Filly. In 2006 he was back in the national spotlight as the trainer of the colt Street Sense who won the 2006 Breeders' Cup Juvenile and the 2007 Kentucky Derby. Now in semi-retirement, Nafzger will only train for two clients, James B. Tafel, owner of Street Sense, and for Bentley Smith, who now has eight horses being trained by Nafzger. Smith's first wife (who died in 1999) was the daughter of Unbridled's owner, Frances A. Genter, and ran the Genter stable before its dissolution.
Inducted to the Texas Rodeo Cowboy Hall of Fame in 2008