The biggest fumble of Matt Leinart's career happened off the gridiron -- the former quarterback revealed he took Rihanna on a date back in the day ... but an unwelcome appearance torpedoed the whole thing.
The ex-USC Trojans superstar broke it all down on his "Throwbacks" podcast with "Entourage" star Jerry Ferrara ... when he reminisced on working with show guest Josh Richman to set up some one-on-one time with the singer at Teddy's nightclub in L.A.
Leinart said the odds already weren't in his favor after two previous attempts .