Leinart spent last season backing up Carson Palmer and Terrelle Pryor for the Oakland Raiders. The former Heisman Trophy winner was drafted in the first round by the Arizona Cardinals and spent time backing up Matt Schaub with the Houston Texans, but has never made much of an impact in the NFL.
But after E.J. Manuel and Kevin Kolb both suffered injuries during the preseason, the Bills had no choice but to turn to the free agent. Rookie free agent Jeff Tuel was the only healthy quarterback on the team's roster, which prompted the Bills to give Leinart and John Beck a workout.
Leinart has the slightly better track record and should provide some stability until Buffalo's quarterbacks get healthy.