Stanley was a first-round pick of the Boston Red Sox in and played his entire 13-year career, 1977–89, with the team. A sinker ball specialist, Stanley was the team's all-time saves leader, a record he held for 20 years, until Jonathan Papelbon tied him at 132 saves on June 29, 2009 and then passed him on July 1, 2009. He is also the Red Sox all-time leader in appearances with 637, relief wins, and is a member of the Red Sox Hall of Fame since. His best season came in when he led the Sox with 33 saves and posted a 2.45 ERA. Stanley was a key member of the Red Sox team that came within one strike of winning the World Series but ultimately fell to the Mets in seven games. Stanley entered Game 6 with the Red Sox one out away from clinching their first World Series since 1918. But his wild pitch to Mookie Wilson allowed the Mets to tie the score, and then New York won Game 6 on Bill Buckner's fielding error that allowed Ray Knight to score from second base. Stanley and the Red Sox would return to Shea Stadium for Game 7, in which the New York Mets would ultimately be victorious by a score of 8-5. In, Stanley was converted to a starterfor the first time since. He went 4-15 with 67 strikeouts and a 5.01 ERA. On September 25, 1989, Stanley announced his retirement. He compiled a 115-97 career-record with 693 strikeouts, a 3.64 ERA, 21 complete games, seven shutouts, 132 saves, and 1707 innings in 637 games. Stanley is the only player in major league history born in Maine to be named to an All-Star game.
Coaching career
Prior to joining the Blue Jays, Stanley served as a minor league pitching coach in the New York Mets' and San Francisco Giants' organizations, including service with the Connecticut Defenders, the Giants' Double-AEastern League affiliate. On December 23, 2011, Stanley was announced as the pitching coach for the Blue Jays' Triple-A affiliate, the Las Vegas 51s. On January 7, 2013, Toronto announced that Stanley would be the pitching coach for their new Triple-A farm club, the Buffalo Bisons. Almost a year later, on January 4, 2014, the Blue Jays announced that Stanley would be replacing Pat Hentgen as their bullpen coach. On December 19, Stanley was named the pitching coach for the Double-A New Hampshire Fisher Cats. On January 19, 2016, Stanley was announced as returning to the Buffalo Bisons. Stanley was confirmed to return for a third season as the Bisons' pitching coach on January 19, 2017.