Groundwork for a research project. I expect the definitions described to change as I develop my argument.

Question: What's the length of a typical baseball career? I wondered, so I checked it using Lee Sinins' Baseball Encyclopedia. The mean (average) career length for a non-pitcher whose last season was between 1940 and 1990 (the dates are convenient for my purposes, but otherwise arbitrary) looks about like this:

• 6.76 seasons.
• 496.9 games.
• 1741 plate appearances.

Let's put a face on that Major League career: Joe Grace. Joe, an outfielder who served as backup catcher in his early years, came up with the Browns in 1938; after that cup of coffee he played about in about half of the St. Louis games for next two seasons and was in the Brownie lineup most days in 1941. He went off to war, returning in 1946. The Browns traded him to the Senators in the middle of the '46 season. The next year he played in about half the Washington games. That's his big league career.

  G   AB    R   H 2B 3B HR RBI SB CS  BB  SO  BA   
484 1561  225 442 76 18 20 172  9 17 179 135 .283 

Stats from Baseball-Reference

Others who had average-length careers:

Player              Seasons   Games  Plate
                                     Appearances
Luis Olmo               6      462    1733
Steve Mesner            6      451    1742
Dick Culler             8      472    1727

A couple notes:

• Adding pitchers into the mix has no particular effect on these averages, which surprised me a little.
• There's a significant era effect: Adding earlier players reduces the averages more than you'd guess (nearly two years), while continuing through the present raises them slightly.
  • That has to be significant. Somebody should research it....