Fantastic Swings and When to Expect Them

The purpose of this post is to briefly examine swing and contact data. Specifically, it will take a look at those players whose swing decisions are most and least impacted by the traditional strike zone. 

Every swing a hitter takes today in professional baseball is a data point. From Summer League auditions to Major League playoff hunts, data is being recorded for each batter’s swing. Of course, a player’s swing is a unique and complex thing; what follows will not delve into those physical dynamics of a swing. Rather, it will consist primarily of the choices players make in deciding when to swing and when to, well, not.

This topic is of heightened meaning today given the stakes for players who manifest various swing tendencies. Given data’s proliferation, these split second (or premeditated) swing decisions are increasingly playing a role in player development and performance evaluation. Is a player ready to make the leap from High-A to AA? Today, that decision might depend nearly as much on his OPS as his contact rate on pitches in the zone, or swing rate on pitches out of it.

Just to get started, here are a couple general relationships between the various swing data given in scatterplots. The data cover 2019 qualifying hitters and originate from Fangraphs’ fantastic stats page.

This first figure likely confirms something many would anticipate: free swingers, or those with higher swing percentages, generally pay for their alacrity in the form of lesser contact rates. However there are exceptions. 

Jeff McNeil has the highest swing percentage in baseball and he is also a front runner for the National League’s batting title. Hanser Alberto, who swings the fifth most often in baseball, makes contact on more than 85% of those many swings. 

Here’s another:

The scatterplot above illustrates another intuitive point: those players who see fewer pitches in the zone also tend to swing and miss at pitches at a higher rate. One might hypothesize that seeing fewer pitches in the zone leads to chases at less than optimal pitches to hit. 

The primary point of including this second visualization is to underscore the fact that not all balls and strikes (or indeed swing decisions for those pitches) are created equal. A hypothetical player may swing and miss quite a bit, but that could partially be a product of the pitches that he’s seeing. When evaluating a player’s swing and contact rates, having context for what is being thrown to them, where, and how often, is crucial. 

In a vacuum, observing swing rates for pitches inside and outside the strike zone is not enough to draw rigorous or meaningful conclusions from. Despite this fact, that is exactly what’s coming next. Here is a third plot, this time comparing qualifying batters swing rates on pitches inside and outside the strike zone.

The orange horizontal and vertical lines indicate the average O-Swing% (swing percentage on pitches outside the zone) and Z-Swing% (swings on pitches inside the zone), respectively. These two rates indicate that 2019’s hitters, on average, swing at pitches in the zone nearly 39% more often than pitches out of it. Given the immense velocity and spin applied to pitches today, that fact alone is worth appreciating batters’ pitch recognition abilities for. 

While this plot illustrates again relatively intuitive data (those who swing more at pitches in the zone tend to also swing more at pitches out of it), it serves primarily as an intermediate step to observing two extremes: players with the widest and slimmest gaps between swing rates across pitches inside and outside the strike zone.

Below is a table populated by those players whose swing rates are closest across balls and strikes, i.e. those who do not discriminate so much based on the traditional strike zone.

Gary Sanchez, this table’s leader, swings at pitches outside the zone just 20% less often than pitches inside the zone. These 15 players all swing at pitches outside of the zone at least 31% less often than pitches in the zone. Remember, the average difference is nearly 39%. Their cumulative swing percentages are pretty typical too. Altogether, these batters swing at 46.47% of pitches while qualifying batters swing at 47.34%.  Still, a few swing very little (see David Fletcher, Brett Gardner, and Daniel Vogelbach).

Now, let’s look at those players whose swing choices really adhere to the strike zone.

The top three on this board, George Springer, Freddie Freeman, and Khris Davis, swing at pitches in the zone greater than 50% more often than those outside of it. That is rather incredible. These hitters force pitchers to come to them and are generally unwilling to expand their strike zones. While the first table of hitters more readily blurs their strike zones in search of pitches to hit, this second cohort more often hunts for obvious strikes.

Here’s the final, less anticipated, point. The strike zone-disregarding “free swingers”, remember, swing at 46.47% of pitches. I, at least, was surprised to find that the “zone-adherents”, on the other hand, swing at pitches roughly 1.5% more often: 47.92%. Figure 1, which illustrates a negative relationship between swing percentage and contact percentage, holds up here. Figure 2’s  correlation, however, does not. It turns out, those “free swingers” who don’t discriminate between strikes and balls so much, swing less often and additionally make contact more often, 5% more often.  

Given the correlative relationship between pitches in-zone and contact rate (Figure 2), it is counterintuitive to see such a divide between those two groups: those who fastidiously wait for pitches inside the zone and those who will swing at a disproportionately high number of pitches outside of it. 

As mentioned above, this line of inquiry is a relatively limited one. At a glance, there looks to be a lot of differences between the players of these extremes than simply their Z-Swing% – O-Swing% (Springer, Freeman, and Davis are decidedly different types of players than Sanchez, Jose Iglesias, and Alberto, for instance). Still, it’s a good example of how baseball constantly wrinkles our expectations.