Closers, like many other relief pitching roles, are a relatively new addition to baseball. ESPN.com points to Bruce Sutter in 1979 as the game's first closer, as he was called upon only when his team was in the lead. Later, in 1988, Oakland Athletics manager Tony La Russa further defined the closer role by using pitcher Dennis Eckersley only in the 9th inning when the A's had the lead. This is how closers are commonly used today, typified by New York Yankees pitcher Mariano Rivera, arguably the best closer in MLB history.
- Bob Nightengale: "'It takes a special person': Baseball Hall of Fame finally home to Mariano Rivera and history's great closers", USA Today, July 18, 2019. 
- Joe Posnanski: "How Sparky Lyle launched the tradition of closer entrance music", mlb.com, April 18, 2018. 
- David W. Smith: "The Myth of the Closer", Reasearch paper presented at the SABR46 Convention, Miami, FL, July 29, 2016. 
- Fran Zimniuch: Fireman: The Evolution of the Closer in Baseball, Triumph Books, Chicago, IL, 2010.