O-Swing% Correlations

As David announced earlier this week, fangraphs now has swing data for hitters, giving us a breakdown of who swings at what and how often. This is just another great resource he’s added to the stat pages. And, as always, more data means a chance for more research.

One of the first things I wanted to look at in this data was the effects of swinging at pitches outside of the strike zone. It’s been a sabermetric credo for a while now that good hitters are selective at the plate and don’t chase pitches out of the zone, but players like Vladimir Guerrero, Nomar Garciaparra, Ivan Rodriguez, and Ichiro Suzuki have all had tremendous careers despite swinging at pitches that no sane person would think they could hit. If you can be a hall of fame hitter without being selective, how important is it?

So, I decided to take the list of qualified hitters for 2008 (197 in all) and look at the correlations between their O-Swing%, which measures how often they swing at pitches out of the strike zone, and their BB% and K% rates. Intuitively, I would have thought that the more often a player swings at pitches that would otherwise be called balls, he’d have a lower walk rate and a higher strikeout rate. Here are the results:

O-Swing%/BB% correlation: -0.67
O-Swing%/K% correlation: -0.10

The walk rate correlation matches up with expectations, as there’s a strong negative correlation between swinging at pitches outside the strike zone and walk rate. This, of course, makes sense – the more often you swing at pitches that would have otherwise been called balls, the less likely you are to draw four balls in any given plate appearance. Guys like Matt Diaz eschew the walk through sheer determination.

However, look at the correlation between O-Swing% and K%. I’d have expected a fairly strong positive correlation, as you tend to think of guys flailing at sliders in the dirt as more prone to strikeouts. However, the correlation barely exists at all, and it goes to the negative to the point that there is any correlation. We see this manifest in guys like Erick Aybar and A.J. Pierzynski, who both swing at 37% of pitches outside of the strike zone but strikeout just 7% and 6% respectively.

It appears that players who swing at pitches outside of the zone do so because they can hit them – it is the ability to make contact that creates the aggressive approach, and not just a player’s desire to hack at anything.