teacher catToday, Javier Baez stepped up to the plate in the top of the 2nd inning and saw two pitches. The first was a change-up out of the zone – he laid off. The second pitch was a fastball in the zone and he hit a powerful line drive … directly into the left fielder. Well, not into him, though it was a rocket. In the top of the 4th, Baez saw three pitches. The first was a breaking ball that just caught the plate – no swing. The second was a breaking ball that missed – no swing again. The third pitch was a slider in the zone that Baez took deep to left field for a home run. Baez’s final plate appearance came the next inning, and he again saw three pitches. The first was a slider low and away – no swing. The second pitch was a fastball at the top of the zone, and Baez fouled it back. The final pitch was a hanging slider in the zone that Baez flies out to left field.

Out of those eight pitches, five were in the zone and three were out of the zone. Baez made contact with four pitches in the zone, laid off two that missed and let one breaking ball strike go by.

As a very small sample, that’s actually pretty encouraging, but we’re not here to discuss Baez’s plate approach, swing changes or projections. Instead, these few at bats reminded me of an important set of statistics: swing rates.

Over the next two nights, I’d like to introduce (or reacquaint) you with some very useful statistics that have to do with plate discipline. Tonight, we’ll take a look at what these statistics are and what they mean, where you can find more on them, and how they express themselves league-wide. Then tomorrow night (tune in!), we will focus our attention on these stats in relation to the 2015 Chicago Cubs.

I’m going to scratch the surface of swing/contact rates for the purposes of this discussion, but for a deeper, more in depth look at swing rate statistics, check out the FanGraphs Library installment here. 

First, here are the terms:

  • O-Swing% – Percentage of pitches a batter swings at outside the strike zone.
  • Z-Swing% – Percentage of pitches a batter swings at inside the strike zone.
  • Swing% – Percentage of pitches a batter swings at overall.
  • O-Contact% – Percentage of pitches a batter makes contact with when swinging outside the strike zone.
  • Z-Contact% – Percentage of pitches a batter makes contact with when swinging inside the strike zone.
  • Contact% – Percentage of pitches a batter makes contact with overall when swinging.

Once these stats are listed out like this, it’s much easier to understand their purpose. In broad strokes, the swing rates are used to measure how often a batter offers at pitches in and out of the zone. Similarly, the contact rates are used to measure how often a batter makes contact with those same pitches.

Based on this description alone, most fans can intuitively understand the usefulness of these stats. Unfortunately, when these stats are used independently, they can be quite misleading.

For example, a batter with a low O-Swing% and high Z-Swing% is good at identifying pitches in the strike zone. Typically, having a good eye is an important quality for a hitter. However, without knowing the contact rate for that hitter, we have only a portion of the whole picture. If that same hitter has a low Z-Contact%, he may have a hole in his swing or a crippling contact issue that limits his overall offensive impact (think Brett Jackson and Mike Olt, when they were struggling, as two examples).

There are several high/low swing rate combinations that can define a player, so be sure to gather all of the data before analyzing it. With the information in tow, you will often be better able to understand why you’re seeing certain performance issues with respect to a player. A guy has terrible numbers? Because he’s striking out too much? Well, is it because he’s started to expand his zone a little too much? Taking too many strikes? And so on and so forth.

Taking a look at the 2014 plate discipline leaderboards, it’s easy to see how these stats can be misused. In the top eight of O-Swing%, we can see sluggers like Jose Abreu, Carlos Gomez and Pablo Sandoval sprinkled around less desirable bats like Chris Johnson and Marlon Byrd. Similarly, the “whole picture problem” manifests itself nicely in the top two O-Contact% leaders, Victor Martinez and Nick Markakis. Both players hit for a decent average, but Victor Martinez hit for about .220 more points of OPS, due to better quality contact – just because you can hit something doesn’t mean you should.

For a little more context, here are some numbers for the 2014 season across all of baseball:

StatTop (min. 300 PAs)
O-Swing%48.1% (Pablo Sandoval)
Z-Swing%82.3% (Carlos Gomez)
Swing%59.5% (Sandoval)
O-Contact%88.1% (Victor Martinez)
Z-Contact%97.3% (Ben Revere)
Contact%92.4% (Revere)
StatBottom (min. 300 PAs)
O-Swing%19.3% (Matt Carpenter)
Z-Swing%49.4% (Carpenter)
Swing%33.1% (Carpenter)
O-Contact%42.3% (Junior Lake)
Z-Contact%68.4% (George Springer)
Contact%61.0% (Springer)

One random lesson? Throw Matt Carpenter nothing but strikes.

If you were unfamiliar with these statistics before tonight, it may take you some time to get used to them – especially considering the numbers aren’t too frequently used. But when they are used correctly, they can be very illuminating. If you’d like to learn more about swing% and contact% you can check out these links here, here, here, and here or you can come back to Bleacher Nation tomorrow night, where I will take these numbers and apply them to the Chicago Cubs.

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