When Greg Maddux said "chicks dig the long ball," I don't think this is what he had in mind. As mentioned in Saturday's game recap, Bronson Arroyo gave up home run no. 40 in a classic Bad-royo outing, allowing 3 taters in one-plus innings of "work" at Coors Field. He became just the 19th pitcher to allow 40 long balls and the first since Eric Milton in 2005. Sort of like losing 20 games, allowing 40 home runs is a perverse badge of honor in that a truly terrible pitcher would never be given the opportunity to face so many batters. The 40 HR club is a distinguished fraternity - four HOFers plus seven other former All-Stars make up the list, and the performances in general are not disastrous.
Arroyo's 2011 is not typical for the 40 HR year, unfortunately. Whereas half of the 22 prior 40 HR seasons had an ERA+ above average, Arroyo's 74 is the second-worst, ahead of only Milton's monstrosity. Arroyo also sets himself apart from the pack in throwing just 175.7 innings to date, the lowest by at least ten innings.
Like any saber-leaning fan I initially thought that bad luck could be at the root of the tater explosion, but that's not supported by the data. According to Hit Tracker, just four of his 2011 home runs (not counting Saturday's) are classified as "Just Enough/Lucky." Five others are "Just Enough." 12 are "No Doubt" and 16 are "Plenty," so it's not as if Bronson has mostly given up a bunch of wall-scrapers. I also considered that some of his 2011 home runs could be doubles or triples of years past, but that also doesn't seem to be the case. Arroyo has allowed 46 doubles/triples so far this year, which is slightly more than either of the past two years (despite more innings in those seasons). So it's not just the round-trippers. Bronson's giving up a boatload of extra-base hits; the home runs have simply been more noticeable.
The cause of the power surge isn't completely clear, but my guess is that it's a combination of failing to keep the ball low in the zone and a slower fastball. The pitch location graphs below are a bit muddled, but to my eye it looks like he's throwing fewer pitches lower in the zone. This is likely the cause for Arroyo's worsening groundball ratios. Arroyo had seemingly become more a groundball pitcher during the past few seasons, learning to rely on an improved IF defense. His GB/FB ratio in 2009-2010 was 0.80 and 0.76 in 2008. But this year it's down to 0.62, about where he was in his first two years in Cincinnati. So not only is he allowing more balls in play, but more of them are being hit in the air. And they're going farther, too - his HR/FB percent has jumped to 12.7% this season after never reaching 10% in prior Reds seasons.
As for his fastball velocity, it's dipped to 87.0 MPH, a full MPH lower than 2010 per Fangraphs. A one MPH difference might be immaterial, but then again Arroyo's poor fastball might have finally crossed below the threshold that allows major league hitters to be honest - especially if it's not kept low in the strike zone.
Can Arroyo turn back the clock next year? Hopefully. Any solution will need to account for the incredible amount of damage inflicted by left-handed batters this year. LHBs slugged about .450 in each of the prior two years against Bronson, but this season it's up to .622. To put that in context, Dan Uggla is slugging .456 this year. No NL hitter is slugging .600. Bronson's contract will mean he'll get an opportunity next season to remedy the wrongs of 2011, but it's far from certain that he'll have his old Tiger Eyes.