What’s Troubling Adrian?

The Red Sox are a disappointing 43-42 this season, in fourth place by a half-game over the Blue Jays, and 8.5 games out of first place in the AL East. However, despite their pitching struggles and numerous injuries, especially in the outfield, the Red Sox are merely 2.5 games behind the Orioles for the second wild card spot. The playoffs are within reach, and as Jacoby Ellsbury gets back into the swing of things and Carl Crawford and Dustin Pedroia return from the disabled list, the Sox could make a serious postseason push. Though it would certainly help if Adrian Gonzalez was hitting at his normal level.

Through 85 games and 370 plate appearances, Gonzalez is hitting a measly .284/.330/.417. While his .322 wOBA meets the league average, he is a far greater hitter. He has a career .371 wOBA and a .395 mark over the last three seasons. Projection systems, which are based heavily on historical data, see him rebounding nicely down the stretch. But there is no guarantee that he completely rebounds and the possibility still exists that he’ll finish the year with a drastically lower wOBA. Whether he finishes the season hovering around a .320 wOBA, or closer to the .340 that ZIPS projects, his current and potential dropoffs are worthy of investigation.

Throughout history, there are plenty of examples of players whose wOBA dropped substantially as compared to their prior three-year averages. Among players who managed 1,000+ plate appearances over four consecutive years, and who batted at least 400 times in the fourth season – to avoid drop-offs due to injuries or reduced playing time – there were 187 such examples of players whose wOBA dropped by 70+ points.

However, a selection bias exists in the data in that players with extremely high wOBAs over a three-year span are more likely to experience larger drop-offs: Roger Hornsby’s .544 wOBA average from 1923-25, and his subsequent .396 mark in 1926 isn’t really a comp for Gonzalez. To get around that issue I restricted the data to players whose three-year wOBA average fell in the .370-.420 range. That dropped the list to 81 players who lost 70+ points of wOBA in that fourth season.

Most of the recent examples are players whose careers were essentially over after that fourth season. Sammy Sosa had a .387 wOBA from 2002-04, and a .292 wOBA in 2005. Roberto Alomar had a .404 wOBA from 1999-2001 and a .316 wOBA in 2002. Pat Burrell had a .382 wOBA from 2006-08 and a .304 mark in 2009. Jim Edmonds, like Gonzalez, had a .395 wOBA from 2004-06, but well to .316 in 2007.

The comparable players might not bode well for Gonzalez, but as Adam Dunn is showing us, sometimes players simply have fluky poor seasons. Among the group whose three-year average fell between .370 and .420, Dunn actually had the second-largest drop-off of all time, with a .385 average from 2008-10 and a .266 wOBA last season. Though his wOBA fell by 119 points, he now has a .370 wOBA and has rebounded nicely.

That being said, why exactly has Gonzalez struggled? According to an excellent post from ESPN’s Sweetspot affiliate Fire Brand of the American League, Gonzalez’s struggles revolve around plate discipline, an assertion backed up by the data. FanGraphs has Gonzalez swinging at 52.6% of his pitches seen, compared to his career 48.7% rate. He hasn’t topped 50% in this category since before he was a regular starter. His rate of swings out of the zone is up to a career-high 37.1%, and his career rate is just 29.1%. He has swung at 75.1% of pitches thrown his way in the zone, up from 69.9% last, but is making less contact on those pitches. And while his overall contact is slightly up, it has come more from pitches out of the zone, where worse contact is often induced by pitchers.

And while he has produced more effectively over the last two weeks – a .393/.404/.500 slash line and a .392 wOBA – some of his plate discipline stats are still askew. That productivity is accompanied by a 41.5% rate of out-of-zone swings, which is disconcerting since pitchers have only thrown 38.2% of pitches in the zone throughout this span.

He has also swung at 57.1% of all pitches, and while his approach has yielded solid results recently, there doesn’t seem to be much in the way of a discernible change. Gonzalez started out slowly and has experienced some recent success despite approaching plate appearances in the same odd way. Perhaps he is being pitched differently and is yet to make adjustments.

The previously linked Fire Brand article found that pitchers are more inclined to challenge Gonzalez inside this year, instead of constantly staying low and away. Since he hasn’t made them pay for it, there hasn’t been any reason to limit their plate coverage. Gonzalez is likely too good to finish the season with merely league average production, but there is certainly precedent for substantial drop-offs in productivity, and his can be traced to a specific root cause. The Red Sox playoff hopes don’t entirely hinge on his production picking up, but given the uncertainties caused by numerous injuries to everyday players, having Gonzalez as anything but a sure thing clearly hurts.