Bennett was born in Birmingham, Alabama. He played halfback and several other positions while attending Ensley High School in Birmingham, Alabama. Bennett was an excellent basketball and baseball player during his high school career. Bennett was an all-state performer his senior year, amassing over 1000 yards while carrying the ball 101 times. Bennett was nicknamed "Biscuit" by friends because he always had room for one more.
After his college career, he was selected by the Colts with the second pick of the 1987 NFL Draft. This draft was deemed the “Year of Linebacker”, but Bennett was considered to stand “head-and-shoulders above the rest.” Bennett was Alabama's highest draft selection since Joe Namath in 1965, and as of 2015[update] remains the highest selected Crimson Tide defender ever.
Bennett and the Colts were unable to come to an agreement on a contract. Bennett was then dealt to the Bills from the Colts in a three way trade that also included Los Angeles Ramsrunning backEric Dickerson, and Bills running back Greg Bell. This trade occurred in the fall of the 1987 season, just before the trade deadline, and has been called "the trade of the decade" by the New York Times.
In the NFL, Bennett's talent at the left outside linebacker position helped the teams he played for to five Super Bowl appearances (four with Buffalo and one with Atlanta), but they lost them all (an NFL record he shares with Glenn Parker). In his 14 NFL seasons, he recorded 71½ sacks, 7 interceptions, 112 return yards, 31 forced fumbles, 27 fumble recoveries, 78 fumble return yards, and 3 touchdowns (1 interception, 1 fumble return and 1 blocked field goal return).
At the time of his retirement, his 27 defensive fumble recoveries were the third most in NFL history.
Bennett was inducted into the Alabama Sports Hall of Fame in 2004.