Alan Marshall Clark (born January 9, 1948) is a former professional baseball umpire who worked in the American League from 1976 to 1999, and throughout both Major Leagues in 2000 and 2001, wearing uniform number 24 when the American League adopted them for its umpires in 1980, then retained the number when the NL and AL staffs were merged in 2000. Clark umpired 3,392 major league games in his 26-year career. He umpired in two World Series (1983 and 1989), two All-Star Games (1984 and 1995), five American League Championship Series (1979, 1982, 1987, 1992 and 1999), and three American League Division Series (1981, 1996 and 2000). Clark worked second base in the 1978 one-game playoff between the New York Yankees and the Boston Red Sox, which the Yankees won 5–4. He was the home plate umpire in Nolan Ryan's 300th career win on July 31, 1990.