Adam Dunn’s Changed Plate Approach

Suffice it to say that Adam Dunn’s power has been eerily consistent throughout his career, hitting 40 +/- 2 home runs the past six years with over 100 RBI in five of them. His OBP, walk rate, and strikeout rate were very similar from 2004 to 2009. However, Dunn showed a change in approach last season, reaching career worsts in walk rate (11.9%) and strikeout rate (35.7%) while his OBP was his lowest since 2003 (.356). Granted, that’s still a very good OBP, but his change in approach came with an OBP drop of 40 points since he first joined the Washington Nationals.

Dunn’s swing rate has increased from 40.4% to 45.0%, a career high, showing a more aggressive approach at the plate. Here’s how his other plate-discipline stats changed:

2009: 19.4% O-Swing%, 65.5% Z-Swing%, 73.0% Contact%, 10.7% SwStr%
2010: 28.5% O-Swing%, 68.3% Z-Swing%, 68.2% Contact%, 13.8% SwStr%

As a consequence of his increased swing rate, Dunn whiffed on more pitches in 2010 mainly due to a 9% increase in swing rate on pitches outside the zone. The drop in contact rate shows that while Dunn swung more, he didn’t make more contact per swing. Swinging on more pitches did allow Dunn to make slightly more contact on a per-pitch basis, as he made contact on 30.7% of 2010 pitches vs. 29.5% of 2009 pitches. It’s also notable that the increased swing rate caused Dunn to see a career low 4.11 pitches per plate appearance compared to 4.32 pitches/PA in 2009. However, the fact to the matter is that Dunn’s OBP, walk rate, and strikeout rate were not favorable changes last season, which are all related results of plate discipline.

To investigate a bit more into Dunn’s changed plate approach, let’s look at how Dunn changed his swing behavior against different pitch types. The following graphs from the batter’s point of view are Dunn’s “50% swing zones” against fastballs in 2009 and 2010, a term coined by Jeremy Greenhouse:

What the swing zones tell you is a quick glimpse of Dunn’s swing rate by pitch location. If a fastball was located within the area, then Dunn is estimated to have swung at the pitch at least 50% of the time. If outside the area, less than 50% of the time. Comparing and contrasting swing zones are a simple way to show how a batter has changed his swinging behavior. It seems that the left-handed Dunn swung at more low fastballs from right-handed pitchers, a more aggressive approach, while swinging at fewer inside fastballs from left-handed pitchers.

Here’s a look at Dunn’s swing zones against breaking balls, not including off-speed pitches such as changeups:

The left graph shows a more aggressive approach against RHP sliders and curve balls in 2010, while the graph against LHP breaking balls show that Dunn started to swing more at outside and high breaking balls more often than low ones.

Let’s see how Dunn’s approach changed by the numbers based on these splits. Here’s a table of Dunn’s plate discipline statistics in 2009 vs. 2010 split by pitcher handedness and pitch type:

	Swing%	O-Swing%	Z-Swing%	Contact%	SwStr%
2009 RHP FB	40.7%	18.7%	63.9%	80.3%	8.0%
2010 RHP FB	43.5%	23.9%	66.5%	73.8%	11.4%
2009 LHP FB	43.9%	21.6%	63.0%	72.8%	11.9%
2010 LHP FB	46.3%	29.0%	64.5%	67.3%	15.1%
2009 RHP SL/CU	33.7%	15.8%	56.5%	62.8%	12.5%
2010 RHP SL/CU	37.1%	24.0%	56.2%	53.9%	17.1%
2009 LHP SL/CU	40.2%	24.6%	58.5%	65.0%	14.1%
2010 LHP SL/CU	41.1%	31.0%	60.2%	63.6%	14.9%

Across the board, Dunn whiffed more often in 2010 because he swung at many more pitches out of the zone. In particular, RHP breaking balls caused Dunn to swing much more often out of the zone while his swing behavior in the zone was almost exactly the same. Contact percentage (per swing) did not justify the change in swing behavior and instead caused Dunn to whiff more and presumably walk less.

One last table for you. Dunn had a slow start in 2010 and while looking at his slash stats by month, I was wondering whether his swing rate by month said anything about his OBP. Here’s a look at how Dunn’s swing rate changed by month in 2009 and 2010 along with his slash stats:

	Swing%	AVG/OBP/SLG	|		Swing%	AVG/OBP/SLG
April 2009	34.9%	.310/.467/.606	|	April 2010	40.2%	.225/.361/.463
May 2009	39.2%	.243/.349/.551	|	May 2010	44.6%	.313/.395/.616
June 2009	38.2%	.241/.389/.437	|	June 2010	47.2%	.275/.330/.559
July 2009	39.7%	.319/.427/.615	|	July 2010	45.2%	.284/.379/.580
August 2009	38.4%	.297/.453/.659	|	August 2010	43.9%	.228/.342/.545
Sep/Oct 2009	45.5%	.212/.322/.333	|	Sep/Oct 2010	40.3%	.227/.333/.432

There actually does seem to be some correlation between Dunn’s swing rate and his on-base percentage by month. Small sample aside, it’s clear that Dunn’s swing rate has increased across the board from 2009 to 2010. Whether that ultimately had an effect on his decreased walk rate and OBP, I believe the evidence says that Dunn’s changed plate approach did not benefit him in 2010.

Of course, this ignores the fact that Dunn is now with the Chicago White Sox, playing in a ballpark that’s much more favorable to left-handed hitting power hitters than when he was with the Nationals. But AL Central pitchers have heard of Dunn’s power, and if they decide to pitch around him (while noting that Paul Konerko will return to the lineup in 2011), Dunn’s pitch recognition will be tested, especially if he continues to be aggressive while swinging at pitches out of the zone. Unsurprisingly, Dunn projects to hit 40 home runs again by most projection systems, but opposing pitchers will use every bit of information they can get to mitigate the damage if they realize that Dunn has indeed changed his plate approach.