Born in Manhassett, New York, Greenfield attended Staples High School Westport in CT. Inspired by such films as Cuckoo's Nest, Risky Business and Something Wild and directors like Oliver Stone and David Russell, he began working with film at the young age of ten.
By the time he was in high school, his work was so impressive that it caught the eye of famed director Steven Spielberg, who wrote Greenfield a long letter urging him to continue his filmmaking.
Following high school, Greenfield took Spielberg's advice and attended the USC School of Cinema-Television as an undergraduate.
Having already made progress in film, he exceeded expectations and was chosen to direct Alive & Kicking. Like his marks, the film was a huge success and garnered him awards from film festivals across the country.
With a BA from the University of Southern California, Greenfield directed the 10-minute short comedy, The Right Hook. During the making of the film, he worked on a series called Go Sick! which filmed sick stunts on people.
Although the series didn't fair well, the short did, winning him the Grand Prize at the Manhattan Short Film festival in 2000 and the Grand Jury Prize at the 2001 New York Indepent Film Festival. He followed up the success with his first feature, The Animal, starring Rob Schneider.