Adam Dunn has been one of the most consistent players in baseball during the past eight seasons. King of the three true outcomes, Dunn could be counted on to post high walk and strikeout rates, and regularly knock the ball out of the yard. From 2004 to 2010, his raw home run totals were eerily consistent: 46, 40, 40, 40, 40, 38, 38. Now? Well, that level of consistency is unlikely to be replicated, since he’s mired in an epic slump, the likes of which he’s never experienced in his career.
Through 66 games and 275 plate appearances, Dunn is hitting a measly .173/.308/.316. His walk rate is in line with his career mark — and his OBP is still high relative to his batting average — but the slash line components sandwiching that rate are downright miserable. Given his propensity to strike out, Dunn never has been known for posting high batting averages. But these days, he’s whiffing at an otherworldly level.
While his batting average on balls in play is low at .262, this isn’t a case of a putrid success rate suppressing otherwise decent numbers. He’s struggling to make contact, and he’s not faring all that well when he does connect.
Entering the season, there were three or four sure things in baseball. Dunn posting a .240+ ISO was one of them.* At .143, though, he’s 122 points below his .265 career average. And while 275 plate appearances is still a small sample, we’re deep enough into the season to start wondering whether he’ll go back to the old Adam Dunn.
While my colleagues have attempted to determine the root cause of his issues, I’m more curious as to how frequently someone has cratered in this fashion.
* – The others would be Jeff Francoeur performing well enough early on to make some wonder if he’d turned the corner (I even did a study on it!); a very good pitcher having his talent questioned due to a fluky BABIP (Matt Garza, Cliff Lee); and someone potentially getting overrated due to a very high UZR in a very small sample (Brett Gardner).
Given his level of consistency and the depths to which his numbers have fallen this year, there are two main questions that spring to mind:
1. How frequently do batters experience such a sharp ISO decline from an established level?
2. How frequently do batters strike out more than 40 percent of the time in a full year?
To attack the first question I pooled together all four-year spans since 1950, and I used the first three years of the span to determine the true-talent-level isolated power mark. The fourth year then was compared to the average. This way I could avoid using a one-year sample to make determinations. The players had to tally at least 1,500 plate appearances during the first three years, though there was no yearly minimum. I figured 1,500 PAs was a sizable enough number that, no matter how the amount was reached, the true-talent-level could be estimated.
Of the 21,640 four-year spans in the sample, only 5,251 met the 1,500 plate appearances minimum. Of the remaining spans in the sample, only 526 involved a player averaging a .240+ ISO during the first three seasons. And of those spans, only 34 saw a player drop more than 100 points in the fourth season. The largest decline belongs to Jim Thome, who was injured during the 2005 season with the Phillies. That dropoff can be explained in his case.
Next on the list is Andruw Jones, whose decline likely came to mind when considering other Dunn-like implosions. Jones averaged a .258 ISO from 2005 to 2007–and then followed that up with a .091 in 2008. That’s a whopping 167-point drop.
Most of the players at the top of the list saw their power decline at the end of their careers. Phil Nevin was mostly done after 2002, and the same can be said of Mark McGwire. Jim Edmonds had little left in the tank after the 2007 campaign, and Sammy Sosa had seen his best days by the time the 2005 season ended. If Dunn remains in the regular lineup without improving his numbers, he’ld be set to enter some rarified air.
One of the major reasons for his struggles is a ghastly strikeout rate. Dunn has struck out in 42.3 percent of his at bats — way above his career average of 33%. Since 1950, only two players (in three seasons) have struck out more than 40 percent of the time while amassing 500 or more plate appearances: Mark Reynolds 2010 (42.3), Jack Cust 2007 (41.5) and Jack Cust 2008 (41.0). Dunn’s contemporaries in the ISO category struck out more in the year of their decline, but their strikeout rates weren’t really starting from a rate as high as Dunn’s had been in the past several seasons.
Dunn might not be totally done: Travis Hafner was at the top of the first leaderboard before his recent bounce-back. It’s just disconcerting in situations like this because of how rare the situation is in the first place.