According to the Major League Baseball archives, fifteen presidents have thrown out the first ball on Opening Day on 55 separate occasions:
William H. Taft (2 times)
Woodrow Wilson (3 times)
Warren G. Harding (3 times)
Calvin Coolidge (4 times)
Herbert Hoover (4 times)
Franklin D. Roosevelt (8 times)
Harry Truman (7 times)
Dwight D. Eisenhower (7 times)
John F. Kennedy (3 times)
Lyndon Johnson (3 times)
Richard Nixon (2 times)
Gerald R. Ford (1 times)
Ronald Reagan (1 times)
George Bush (3 times)
Bill Clinton (3 times)
The tradition began with William Howard Taft on April 14, 1910, at Washington's Griffith Stadium (Senators vs. Philadelphia Athletics).
Though no special ceremonies were planned, the president was asked by umpire Billy Evans to
throw the ball over the plate immediately following the introductions of the rival managers, Jim McAleer of the Senators and Connie Mack of the Athletics.
The most recent "first ball" thrower was Bill Clinton on April 1, 1996, at Baltimore's Oriole Park at Camden Yards (Kansas City vs. Baltimore).
The only president since William Howard Taft not to throw out a first ball on Opening Day was Jimmy Carter (who did throw out first balls for the Atlanta Braves while governor of Georgia). Franklin D. Roosevelt had the most total appearances with eight. Harry Truman made seven consecutive appearances (1946-1952). Richard M. Nixon (1973 at Anaheim, Calif.), Gerald Ford (1976 at Arlington Stadium, Texas), Ronald Reagan (1984 at Baltimore's
Memorial Stadium) and George Bush (1989 at Baltimore's Memorial Stadium, 1991 at Texas'
Arlington Stadium, 1992 at Baltimore's Oriole
Park at Camden Yards) were non-Washington 'first ball' throwers.