Troy Franklin O'Leary (born August 4, 1969) is an American former professional baseball outfielder who played with the Milwaukee Brewers (1993-1994), Boston Red Sox (1995-2001), Montreal Expos (2002) and Chicago Cubs (2003).

[3] O'Leary made his Major League debut for the Milwaukee Brewers in a home game at County Stadium on May 9, 1993 as a defensive replacement in left field against the Boston Red Sox.

One of the greatest performances of O'Leary's career and in Boston Red Sox postseason history took place on October 11, 1999 in the decisive game 5 of the 1999 American League Division Series versus the Cleveland Indians.

O'Leary responded by sending the first pitch he saw, a Charles Nagy breaking ball, 417 feet over the right field fence for the first grand slam in Red Sox post-season history, giving Boston a 7-5 lead.

With John Valentin standing on second and first base open, Hargrove again chose to intentionally walk Garciaparra to get to O'Leary, this time with Paul Shuey on the mound.

O'Leary's 7 RBI, along with 6 no-hit relief innings from Pedro Martinez, helped to seal the victory and advanced the Red Sox to the 1999 American League Championship Series against the New York Yankees.