In ML baseball and other professional sports, after a team has a
losing season, or a streak of them, the manager is fired. It would be
more satisfying to fire the team, but that is not practical. My
question is: In the past 55 years, has any MLB manager retired or
resigned voluntarily, that is, not under pressure?
Possibly Casey Stengel?

Hello,

Several managers have quit voluntarily. Among them:

Tommy Lasorda of the Dodgers, who opted to move to the front office.
Source: CNN, "Dodgers Manager Lasorda Retires"
http://www.cnn.com/US/9607/29/lasorda.retires/

Tom Kelly of the Twins
Source: Ticker, "Twins manager Kelly retires after 15 seasons with
team"
http://www.allsports.com/cgi-bin/showstory.cgi?story_id=21913

Dick Williams of the Padres quit in protest of the team owner's
meddling
Source: Baseballlibrary.com, "Dick Williams"
http://www.pubdim.net/baseballlibrary/ballplayers/W/Williams_Dick.stm

Whitey Herzog quit the Cardinals in 1990
Source: Bernie Miklasz, "A Ballclub Divided"
http://www.stltoday.com/STLTODAY/SPORTS/SPECIAL/OZZIESMITH.NSF/other/BD3A1B0A08DF0BD786256C0000764A18?OpenDocument

Sparky Anderson quit the Tigers twice in 1995 -- once in protest of
plans to employ replacement players, then permanently later that year
Source: Baseballlibrary.com, "Sparky Anderson"
http://www.pubdim.net/baseballlibrary/ballplayers/A/Anderson_Sparky.stm

Casey Stengel retired from the Mets due to a bad hip in 1965.
Source: Baseballlibrary.com, "Casey Stengel"
http://www.pubdim.net/baseballlibrary/ballplayers/S/Stengel_Casey.stm

I hope this answer meets your needs. If not, please request
clarification.

Search strategy:

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manager retired baseball
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Dick Williams 1973
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Whitey Herzog 1990 quit
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Sparky Anderson 1995 quit
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mwalcoff: Thanks, excellent answer.
knowitall22

Wow.  Quite the question.  For reference, here is a listing of MLB
managers and their tenures:

http://www.sports-wired.com/mlb/managers/

-THV

Knowitall --

This may raise quite a debate.

Last summer Charlie Manuel of the Cleveland Indians resigned after
requesting a multi-year contract and being refused.  (The Indians have
a new general manager, Mark Shapiro, who wanted to consider his
options at the end of the year.)

Was Manuel under pressure?  Not really, though the Indians were
playing under .500.  It was a rebuilding year for the team, so Shapiro
had said repeatedly that he was pleased with the job Manuel was doing.

Best regards,

Omnivorous-GA