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June 6, 2007

The Big Picture

Graying Offenses

by David Pinto

No doubt about it, hitters are getting older. A little over two months into 2007, the average age per plate appearance sits just below the all-time high achieved in 1945, when most young men were off fighting World War II. Why is age going up among hitters, and what are the implications for baseball?

Age per plate appearance measures not just the distribution of age on a roster, but the actual use of older players by managers in a lineup. To calculate this statistic, multiply seasonal age (age before July 1) by the number of plate appearances by the player. Sum those for each player who batted in a season, and divide by the total plate appearances. The following graph shows Age per PA by year from 1901 through 2007:

Since the start of the twentieth century, baseball spent many years with an average age for batters approximately between the 28 to 28.5-year mark. A big dip began in 1909, and reached bottom in 1912-1913. According to The New Bill James Historical Abstract, baseball was expanding the number of players used at that time, and managers started using specialized players like pinch hitters and relievers more. As rosters expanded, it's possible they were filled with younger players. Baseball attendance growth was low in this time period, with a number of leagues folding later in the decade. In a down period, young players tend to be cheap labor, so that may be a contributing factor as well.

After that, with the exception of World War II, average age stayed in a narrow band for about forty years. With the advent of expansion, player ages plunged in the 1960s. The 100 new jobs gave opportunities to cheaper, younger talent. The 1960s was also a low-growth decade for attendance. Baseball during this era was also at the height of control of players. The implementation of the amateur draft removed the chance to sign with a team for a bonus before entering into the reserve system. No mechanisms existed to force the salaries of older players higher. If a team decided to cut the pay of a veteran, he could sign or leave, and it looks like many decided to leave.