Thomas entered Negro League baseball as a second baseman before being moved to the outfield by Detroit Stars manager Bruce Petway in 1922. He quickly gained the nickname Hawk as a sharp-eyed hitter and a far-ranging centerfielder. He consistently hit for power, and he ran the bases with skill and speed. In 1923 he began a six-year stay with the Hilldale club, and was a key player in their 1923-25 Eastern Colored League championships.
In 1929 Thomas hit .322 as a Bacharach Giant, then starred for the 1930 New York Lincoln Giants. He joined the New York Black Yankees in 1931, spending much of the remainder of his career with them. He ruined the 1932 unveiling of Greenlee Field by scoring the only run and making a spectacular, game-saving catch in the Black Yankees’ defeat of Satchel Paige and the hometown Pittsburgh Crawfords. Thomas’s performance prompted Crawfords outfielder Ted Page to remark, “Clint could chase that ball into another world.”
Compiled figures indicate that Thomas’s lifetime average was in the .326 range. He played six years in the Cuban Winter League, batting .310. In four exhibitions against white major leaguers, he hit .417 (5-for-12).