Clark first cut his teeth on the Major League level with the San Francisco Giants in 1975, and he had his first 20 Home Run year in 1978. That season, Clark was named to the All-Star Team, and he would again the following year. Clark had four 20 Home Run years for the Giants, and he would then join the St. Louis Cardinals, where he spent three seasons, two of which were All-Star years.
In that latter year, Clark led the National League in Walks, which was shocking considering that his 136 free passes were more than 46 than he ever had. He led the NL in On Base Percentage with .459, and he had an OPS of 1,055. Clark finished third in MVP voting, his highest ever. The slugger had been in the top ten in MVP voting three times before, but this was his highest finish.
Clark went to the Yankees in 1988, and he was with the San Diego Padres for two seasons, where he again led the league in Walks, while belting at least 25 Home Runs. After a pair of seasons with the Boston Red Sox, he retired in 1992, with 340 career Home Runs. Had Clark developed his ability to gain Walks earlier in his career, he might have gained Cooperstown admission.