Drafted in the eighth round (110th overall) of the 1964 NFL Draft from Morgan State, Leroy Kelly confronted an extraordinarily challenging endeavor: succeeding Jim Brown. After dedicating two seasons as a distinguished contributor on special teams and serving as Brown's understudy, Kelly assumed the starting position when Brown unexpectedly retired prior to the 1966 season. Over the subsequent eight years, Kelly accomplished the remarkable—establishing his own distinguished career and affirming his status as a Hall of Fame athlete.

Kelly relied on exceptional balance, rapid first-step acceleration, and uncanny vision. Rather than overwhelming defenders with raw power, he excelled at setting up blocks for Cleveland's signature trap plays and perimeter sweeps, using subtle hip shifts to avoid tackles in the open field. His dual-threat versatility as a ball-carrier, pass-catcher, and return man made him a constant scoring threat from anywhere on the turf.

Kelly made an immediate impact as a full-time starter in 1966, rushing for 1,141 yards while leading the NFL with 15 rushing touchdowns and a 5.5 yards-per-carry average. He subsequently achieved consecutive NFL rushing titles in 1967 (1,205 yards) and 1968 (1,239 yards). During this exemplary three-year period from 1966 to 1968, he led the league in rushing touchdowns each season, accumulating a total of 42 touchdowns on the ground.

His consistency garnered him six consecutive Pro Bowl selections (1966–1971) and four First-Team All-Pro honors (1966–1968, 1971). Even as defensive strategies evolved to focus on stacking the box against Cleveland, Kelly persisted as the offensive key player, achieving three additional seasons with over 800 yards between 1969 and 1972.

Kelly finished his amazing ten-year journey with the Cleveland Browns after the 1973 season. When he retired, he had amassed 7,274 rushing yards, placing him just behind legendary players Jim Brown, Joe Perry, and Jim Taylor on the NFL's all-time rushing list. His remarkable contributions were honored in 1994 when he was inducted into the Pro Football Hall of Fame. Later, in 2010, Cleveland proudly welcomed him into the first-ever class of the Cleveland Browns Ring of Honor, celebrating his lasting impact.

Overall, Kelly had 7,274 rushing yards and 74 rushing touchdowns, while adding 2,281 receiving yards, 2,774 return yards, and 90 total touchdowns.