He attended Beloit Memorial High School where he played football and basketball, and was on the track team.
[citation needed] After attending Trinidad State Junior College for two years, where he had a successful career, he became the first African-American varsity football player at the University of Colorado at Boulder, joining the Buffaloes in September 1954.
Colorado coach Dallas Ward made the decision to bring black players to the team.
[2][3][4] As a junior, he was an honorable-mention All-Big 7 conference performer,[2] when he was second in the league with 407 receiving yards[5], during a run-oriented era.
[6][7] Trailing 14–0 against the University of Missouri and needing a tie or a win to clinch a berth for the 1957 Orange Bowl, Clarke scored 2 second half touchdowns.
The coach appreciated his speed, soft hands and his ability to run precise routes, so he was converted into a split end.
[citation needed] Mostly a backup behind Billy Howton and Fred Dugan,[14] he appeared in 8 games (3 starts), registering 9 receptions, 290 yards, 3 touchdowns and a 32.2-yard average.
[16] Additionally, he began a streak of seven consecutive games with at least a touchdown reception, which still stands as a Cowboys record shared with Bob Hayes (1965–1966), Terrell Owens (2007), and Dez Bryant (2012).
[citation needed] He turned out to be the Cowboys' first bona fide long-ball threat—before "Bullet" Bob Hayes joined him.
[citation needed] He is also credited as the first African American star athlete, on a Cowboys team that played in a then racially divided Dallas.
[20] On September 23, 1962, Clarke was part of an infamous play where, for the first time in an NFL game, points were awarded for a penalty.
The Cowboys were holding in the end zone on a 99-yard touchdown pass from Eddie LeBaron to Clarke, and the Pittsburgh Steelers were awarded a safety, helping them win the game 30–28.
[22] In 1964, he caught a career-high 65 passes (then a franchise record, now tied for 52nd[23]) 973 yards, 5 touchdowns and received first team All-Pro honors from the Associated Press, and second team honors from the Newspaper Enterprise Association and United Press International.
Clarke remained productive and became a clutch third down receiver, recording 26 receptions for 355 and 4 touchdowns (while Norman caught only 12 passes for 144 yards).
[35] It has also been stated he had the team record for the most career receiving multi-touchdown games with 9, until it was broken by Dez Bryant in 2014.
[2][39] Dowler caught two touchdown passes that day, while Clarke had two receptions, and one rushing attempt for negative yardage.