The Trojans lost their final three games, including a defeat in their first game of the Pac-12 tournament. Starting center Dewayne Dedmon and backup big man James Blasczyk were suspended indefinitely and missed the league tourney following allegations the pair was involved in a melee in Spokane, Wash., during the team's final Pac-12 road trip of the season.
Cantu's status wasn't immediately clear. He has been on the Trojans' staff through four coaching changes and is the longest tenured assistant in the Pac-12.
O'Neill had a 48-65 record during 3½ years at the private school known primarily for its powerful football program after going 6-26 last year while setting a USC record for losses.
The move is a big step up for Enfield.
FGCU has about 11,300 students, plays in a 4,500-seat arena and has only existed for 16 years; USC has 37,000 students, the Trojans play at 10,258-seat Galen Center, and the school has a long tradition of sports success, especially with its nationally ranked football team.
The basketball team has long played in the shadow of cross-town rival UCLA, which hired Steve Alford from New Mexico on Saturday.
USC hasn't made the NCAA tournament since 2011. The Trojans are 12-17 all-time, with their best results coming in 2007 and 2001, when they lost in the regionals, and in 1954, when they lost in the national semifinals.
Before going to FGCU, Enfield was an assistant at Florida State from 2007-11, where the Seminoles made the round of 16 in 2011. He began his coaching career in the NBA as a shooting coach for the Milwaukee Bucks from 1995-96, and was an assistant with Boston from 1999-00.
Enfield's wife, Amanda, drew attention during the NCAA tournament for her model-looks. The couple has three young children.