Adam Dunn's Red Flag?

If Adam Dunn never plays another home game in Washington, his career at Nationals Park ended on a particularly ignominious note: 0-4, 4Ks. The golden sombrero. Of course, he didn't get cheated on any of those swings, so it's not hard to believe than Adam was pressing to give the home fans a memorable show. Dunn's 2010 has been marked by his traditional display of power - 38 homers and counting - but marred by a career low walk percentage and a career high percentage of strikeouts.

Dunn is famous for being very nearly the platonic ideal of a 3 True Outcomes hitter. When he comes up to bat you can lay good money on a home run, a walk, or a strikeout. He has seven consecutive seasons of at least 38 HRs, and averages 111 BBs and 183 Ks per season for his career. He's led the league in strikeouts three times and walks once. Yet in 2010 he has just 76 walks and is one whiff away from a career high of 196 strikeouts.

Over his career Adam has a K/BB ratio of 1.65. This season he's averaging 2.57 strikeouts per walk. His previous season high was 1.95 K/BB through 66 games in his 2001 rookie season. That was also his career low for walk percentage, when 13.3% of all his plate appearances ended in a base-on-balls. In 2010 he's walking just 11.9% of the time. Dunn is also striking out in more than 30% of his plate appearances, the highest that number has been in his 10 year career. As a result Adam's on-base percentage (.359) is the lowest it's been since 2003 (.354) and 22 points below his career average (.381).

The decline can be traced to a second-half slump. Pre-All Star break Dunn was hitting 288/372/588. He's a career 254/385/547 first-half hitter, so apart from swapping some OBP for increased power and batting average, the numbers are pretty typical. In the second half everything declined. Adam typically wears down over the course of the season, but this year it was particularly noticeable. Dunn's batting average cratered to .227, his on-base percentage dropped thirty points to .342 and he lost power to the tune of a .480 slugging percentage (vs. 247/376/493 in the second half for his career.)

At this point it's important to pause and note that there is nothing wrong with a .359 on-base percentage. Dunn's OBP is the 23rd best in the National League, nothing to sneeze at for a guy who also owns the league's 5th best slugging percentage. However, as the Nationals contemplate re-signing Adam for 3 or 4 more years they should be aware of that his 2010 numbers are moving in the wrong direction. It's impossible to draw definite conclusions from a half season's worth of stats, but that doesn't make them any less concerning.

There are mitigating factors. Josh Willingham, who hit behind Dunn in the first half and was arguably the Nats second best hitter in April and May got hurt and struggled in July and August before going on the DL. Maybe his absence made pitchers less reluctant to pitch to Dunn in the second half. Maybe Adam felt more pressure to swing and try to put the ball in play with a rotating cast of Bernadina, Rodriguez and Morse hitting behind him. Or maybe we're seeing the very early signs of Dunn's decline. Hitters with "old player skills" (i.e. power and batting eye) have a nasty track record of declining hard and fast once they hit the wall.

Adam Dunn will probably never be more than a serviceable but solidly below-average defense first baseman. His value is linked inextricably to his bat. He is without question one of the premier sluggers in baseball. But this year his declining walks and increasing strikeouts have driven him closer to being an "all or nothing" hitter. That could be a one-half season blip, or it could be a sign of things to come. I wish Mike Rizzo all the best of luck in trying to figure out which explanation is closer to the truth.

(If you want to check my math, Adam Dunn's stats are drawn from Baseball Reference - a statistical gold mine.)