MASH Report: Turf Field Aging Curve

Andre Dawson became a free agent after the summer of 1986 and he had just one request, his new home field must have grass. After 10 years of playing on Montreal’s artificial turf, Dawson’s knees were destroyed forcing him to move to from center field to a corner outfield spot. I saw him in the 2012 All-Star celebrity softball game and it was painful to watch him move. No one knows for sure how much production was sapped from Dawson by the turf, but I will try to find out. Today, I am going to look into the past and possibly future on playing on how turf ages a player.

The complaints of playing on turf aren’t limited to just past players. Earlier this season Kevin Kiermaier mentioned that the turf at Tropicana Field may be leading to tightness in his hip.

Could it have been caused by playing on Tropicana Field’s unforgiving turf?

“Yes and no,” said Kiermaier, who returned to the lineup Monday against the Red Sox.

Kiermaier said he prepares each offseason for the pounding his legs will take on the AstroTurf.

…

But, Kiermaier added, “The turf, it does do some crazy things to our bodies every now and then. Some days you can feel great and a couple of days later, you don’t change anything, and your body feels awful.”

While teams not playing on grass has shrunk to two, Tampa and Toronto, players still comment/complain about it. With both of the current teams, they have don’t use the old rubbery turf, but a form of field turf the effects may be different.

To start with, here are the teams who used a non-grass turf and when it was installed

As a general rule, AstroTurf was installed in the early 70’s and then removed around 2000. With most teams eventually getting rid of the old AstroTurf and moving to a field turf, I will look at the aging curves from 1966 to 2004 and then from 2004 to current. Here are the curves for wRC+ which will show how the overall batting contribution changed over the years.

Note: The aging curve was created by the delta method by weighting plate appearances using their harmonic means. With this method, there’s a small survivor bias summarized by Mitchel Lichtman at the Hardball Times:

… survivor bias, an inherent defect in the delta method, which is that the pool of players who see the light of day at the end of a season (and live to play another day the following year) tend to have gotten lucky in Year 1 and will see a “false” drop in Year 2 even if their true talent were to remain the same. This survivor bias will tend to push down the overall peak age and magnify the decrease in performance (or mitigate the increase) at all age intervals.

It can be seen that old turf was worse on the body. At age 36, the players on turf aged (i.e. got worse) by an additional 10% compared to players on grass. Looking at the current players from Tampa and Toronto, they basically aging the same as the overall population or just a little better.

I went back to the earlier curve and looked at some fantasy relevant stats. All the signs point to players losing most of their value from declines in speed. Stolen bases declined faster. BABIP dropped faster and therefore AVG. There was a decline in ISO, but it can be attributed to a drop is player speed. It is tough to know if the decline continues with the new turf fields

Looking back historically, turf fields have caused players to age more than expected especially relating to aspects involving speed. The semi-recent use of field turf, the higher rate of aging has apparently disappeared.