A brief survey of where other teams got their present closers. I've omitted a team's saves leader if their WXRL was below 0.
Baltimore: Chris Ray (4.255)
Acquired: 2003 Draft (3rd Round)
Ray was a starter as late as 2004; he got his first significant relief experience in 2005 with Bowie (AA). Ray's first major-league experience also came in 2005, when he pitched in a setup role for the Orioles. When BJ Ryan left for Toronto, he assumed the closer's role and didn't look back.
Boston: Jonathan Papelbon (6.595)
Acquired: 2003 Draft (4th Round)
Like Ray, Papelbon was a starter until 2005, although he did have some relief experience in college. He pitched out the of bullpen the second half of 2005, and was made the closer to start the 2006 season. He responded by having an incredible season, second only to Francisco Rodriguez in WXRL.
New York: Mariano Rivera (5.322)
Acquired: Signed as amateur free agent, 1990
Certainly the best closer of this generation and most likely the best closer in history, Rivera was a starter until 1995, when he was shifted to the bullpen to serve as John Wetteland's setup man. After Wetteland left after the 1996 season, Rivera inherited the closer role. You know the rest.
Tampa Bay: Tyler Walker (0.032)
Acquired: Trade, 4-28-06
Walker came to Tampa via a minor trade, and became the Devil Rays' nominal closer. Before this season, he was a replacement-level reliever. He still is.
Toronto: BJ Ryan (5.987)
Acquired: Free Agent, 11-29-05
Ryan signed a lucrative deal with Toronto just one season after becoming a full-time closer. Unlike Papelbon, Rivera, or Ray, Ryan was a reliever in the minors, first in the Cincinnati organization, and after a trade, the Oriole farm system.
Chicago: Bobby Jenks (3.939)
Acquired: Waivers, 12-04 (Angels)
Jenks had talent, but also off-the-field issues. The White Sox took a chance on him, and put him in the bullpen in the minors. He thrived at Birmingham, and continued his success with the big-league club all the way to the World Series.
Detroit: Todd Jones (2.280)
Acquired: Free Agent, 12-05
The Tigers got burned the year before with Troy Percival, so getting a healthy season out of Jones is a small victory. He's not the best pitcher in the bullpen by a longshot, but he's been fairly effective closing out games.
Jones got a multi-year deal thanks to a comeback season with the Marlins in 2005, his first closer gig since 2001.
Minnesota: Joe Nathan (6.550)
Acquired: Trade, 12-03
In one of most lopsided trades of the decade, the Twins dealt tempermental catcher AJ Pierzynski to the Giants for Francisco Liriano, Boof Bonser, and Nathan. Joe had been a setup man for the Giants, and once given the chance at closing took to it extremely well. One of the top 3 closers in the game.
Los Angeles: Francisco Rodriguez (6.995)
Acquired: Amateur Free Agent, 1998
He burst onto the baseball map with an incredible 2002 postseason, and immediately settled in behind Troy Percival as the Angels' Vice-Closer. When Percival left after the 2004 season, Rodriguez was promoted and has been one of baseball's best ever since. He's younger than Andrew Brown, if that means anything.
Oakland: Huston Street (3.284)
Acquired: 2004 Draft (1st Round)
Street was a closer in college, and only took one year to make the majors. When Octavio Dotel went on the DL in 2005, Street took over, posting a 1.72 ERA and winning the 2005 AL Rookie of the Year Award. He wasn't quite as dominating in 2006, but still was very effective.
Seattle: JJ Putz (5.654)
Acquired: 1999 Draft (6th Round)
Putz was pressed into the closer's role this year after Eddie Guardado struggled. Putz had been tried there before, but with inconsistent results. This time, he was much better, saving 36 games for the Mariners.