Taking a Look at Swing and Contact Aging Curves

Aside from pedigree, why do we think batters will perform better as they move from their fledgling opportunity into and through their prime? Well the easiest way to think of this is the following chart:

Over time players become smarter as they pick up on more and more of the nuances of the game. What you can get away with and what you can’t, but Father Time is still undefeated. As a player gets older they lose their physical superiority to younger players. The boxed area represents the idea of prime where a player has enough mental and physical ability to be one of the best players in the game. Prior to this period they can get by on physical gifts and post they can get by on savvy veteran guile, but within the box is when they’re best positioned to be all that they can be. This isn’t just a baseball thing, but all sports or contests which require physicality or even dating follow this same principle.

This is probably old hat for many of you, but the reason I have delved down this road as that I wanted to take a deeper look into this idea using a couple of statistics from Fangraphs as a proxy for mental and physical ability. I’ll be using the Pitch F/x Plate Discipline Out of and In Zone Swing and Contact rates that they host and I find to be a bit more stable the further we go back as compared to the non-Pitch F/x stuff they track. The data range runs from 2007 to 2013 and I am only looking at players that had 100 or more plate appearances within that aged year.. I needed to download the data for each and every age range to get this just right, which was tedious, so e-mail me if you would like the workbook.

Note: I am well aware of the existence of survival bias and have little doubt that this bias is acting upon this data. However, I have neither the time nor inclination to adjust for this so I leave that to my more dedicated and, well, better, colleagues. I have never seen someone break the ice on this topic so allow me to be the auger and you can come through and really crack ‘er open.

First things first, I’m the realest we need to decide upon which ages we want to look at. Knowing what Mike Trout and Bryce Harper did at 19 doesn’t really tell us a ton about the population and large and the same goes for Omar Vizquel at 45. Here’s a look at number of plate appearances by age for this group:

We see what a geologist would call a drumlin. A hill with a very steep side and then a much more gradual slope on the other side. This study will focus on the years where there were at least 10,000 PA so we’re talking about ages 22 – 38. This should give us a nice, robust sample size for each age.

Next, I found the weighted average totals for each age group and played around with finding a trend line that approximated best fit. Let’s start with the side that I think makes for a good proxy for the mental-side of a plate appearance:

Note that this is incredibly zoomed in, but I think it’s pretty easy to follow everything with the color codes. We see tight and predictable distribution in the O-Swing curve with a very strong R^2 value. What we see seems in line with our hypothesis and it reminds me of a great story (NSFW):

Players gradually learn to chase out of the zone less, settle into a nice mesa during their prime and then tend to see a little giveback before becoming uber-selective. Swings at pitches in the zone follow a very similar arc with the young bulls coming into the league wanting to swat everything before realizing that even pitches within the zone might not be the best medicine if it’s not in a good place for their swing. So we see that first dramatic adjustment and then guys fall into line more or less before we see the passivity that comes with age after years of experience dealing with hurt and loss and the fragility of life.

It’s interesting that the young bulls show more of a gradual decline in O-Swing, but such a dramatic fall off in Z-Swing before settling in, a bit. What we’re seeing, so far, seems only to confirm our thought that as players age they become more selective, ergo, smarter. Let’s flip over to our stand in for physicality, the ability to make in-play contact:

Here we see some really interesting overlap at the inflection points of 28 and 36. This is probably a bit of a right-ward shift from the traditional thoughts of prime (mid to late 20s), but it’s interesting to see these curves move in opposite directions. Again, the R^2 values are very strong, but I think these curves seem to disprove the theory as players are able to make better contact later into their careers. The In-Zone Contact curve does show some give back, but it’s later in the sample than we would think physical losses would have begun to manifest.

There is a very slow incline for O-Zone contact% that slowly picks up steam and then jumps off the charts as a player segues from early to mid-30’s. Meanwhile, we see a much more dramatic swing (tee-hee) for zone contact. There’s two reasons for this; 1) players get better at making contact on pitches in the strike zone as they get older and more mature, or 2) players that can’t make in-zone contact weed themselves out before they get to their late-20s. I’m inclined to put more weight behind the latter, though I’d love to see further research on this idea.

Maybe this is all masturbatory, but I think this is an exciting topic that hasn’t been covered enough. The essence of the game is the 1v1 battle that happens on every single toss as the pitcher tries to get the batter to expand and the batter tries to make the pitcher contract each other’s zones. I’d love to see someone run with this ball so reach out for the spreadsheet or do your own study however you see fit. Thanks for reading.


About Jason Hanselman

Rays fan.
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