What’s Fueling Adam Dunn’s Resurgence?

After suffering through an abysmal 2011 season, White Sox designated hitter Adam Dunn is off to a fantastic start this year.

Last season, the 31-year-old Dunn put up a career-low .266 weighted on-base average (wOBA), or 59 wRC+, in nearly 500 plate appearances. His on-base percentage — which normally was a strength for the slugger — was .292, or 62 points below his previous career low when he was 23. Most disturbing was the sudden disappearance of his power. Dunn has always been a high-strikeout, high-walk, high-slugging player. But last year, Dunn posted an isolated power of only .118. To put that into perspective, consider this: Dunn’s ISO was only two points higher than Nyjer Morgan’s (.116). Dunn also saw his HR/FB ratio drop to 9.6% in a hitter- and home-run-friendly park. His previous career-low was 17.8%, all the way back in 2002.

But now? Well, we’re seeing the old Adam Dunn. Through May 7, he has managed a .394 wOBA, which is fueled by a .364 OBP, .321 ISO and a 28.1% HR/FB. And both the ISO and HR/FB numbers are better than his career highs. The obvious question is whether these numbers are sustainable. Given how quickly outcomes like BB% and HR/FB stabilize, there’s a good chance that Dunn’s end-of-season numbers could be similar to what they are today. The question I have is what is Dunn doing differently? To get a better handle on this, I took a look at Dunn’s performance on specific pitches in different locations.

With a methodology that I’ve used previously, I compared Dunn’s 2011 and 2012 performance by calculating the wOBA per pitch in different locations using PitchFx data. The chart below compared Dunn’s overall performances for those two seasons:

Even without producing a chart that shows the wOBA/pitch differential in each quadrant, it’s obvious where the biggest change has occurred. Dunn is absolutely crushing balls down the middle of the plate. Remember, taking a strike is comparable to making an out when calculating wOBA in this way — and pitches down the middle are rarely called balls. So the positive run values that Dunn is creating in this zone is solely attributable to making pitcher’s pay for throwing pitches in the fat part of the zone.

Dunn isn’t seeing more pitches in this zone (actually .4% fewer than 2011), but he’s attacking these pitches at a higher rate. Last year, Dunn took more than 30% of  the pitches thrown down the middle. This year? He has dropped his take percentage by 10%.

Dunn also is making the most of fastballs he sees in this zone. In 2011, Dunn seemingly lost the ability to handle fastballs and posted a wOBA per fastball of .104. That’s compared to .152 so far in 2012. The biggest difference? Once again, it’s in the heart of the strike zone:

What accounts for the change? I’m not sure. Late last season, in an interview with David Laurila, Dunn suggested that his problems may have been due to adjusting to the new league:

“I’ve been using a lot more [scouting reports and data] because this is my first time in the American League. I have to rely on stuff like that. I didn’t much before, because I knew the pitchers. And if I didn’t know the pitcher, I kind of knew the team’s philosophy on how they wanted to pitch me. That made it a little easier.”

Being less sure of how pitchers will attack you can make batters more hesitant, leading to fewer swings and weaker contact.

Regardless of the reason, it’s clear that Dunn’s resurgence against the fastball has fueled his numbers early this year. Dunn has been more aggressive, which has led to an increase in his whiff and strikeout rates, but the net results have been numbers that reflect the hitter the White Sox thought they were getting when they signed him as a free agent.

In terms of the sustainability of these numbers, there’s one aspect that should give us pause: Dunn’s platoon splits. While he has improved versus his performance last year, Dunn is still below his career average against left-handed pitchers.

In 2011, Dunn’s OBP when facing left-handed pitchers was 108 points below his career average. His ISO (-.200) and wRC+ (-105) were also drastically lower. Early this year, Dunn has improved those numbers against lefties — but as the table below shows, his performance still significantly trails his career norm.

Season	Split	BB%	K%	OBP	OPS	ISO	wRAA	wOBA	wRC+
Career-2011	vs L	-3.50%	-3.80%	0.108	0.465	0.200	37	0.165	105
Career-2012	vs L	-1.90%	-9.40%	0.080	0.344	0.144	27	0.123	75
2012-2011	vs L	-1.60%	5.60%	0.028	0.121	0.056	10	0.042	30

So while there are reasons to believe Dunn has righted the ship, his performance against lefties leaves a pretty big question mark. If he doesn’t improve against southpaws — and his blistering performance against right handers  (.467 wOBA in 2012, .388 career) comes back to earth — Dunn’s regression later this season could be a harsh one.