After eight years of fairly steady decline in power across the league from 2006 to 2014, power numbers returned in a significant way in 2015. Non-pitcher ISO increased 16 points from .138 in 2014 to .154 in 2015 as home runs became more frequent; non-pitchers hit 713 more home runs in 2015 than in 2014. This season saw nine players hit at least 40 home runs, the most 40-home-run campaigns in one year since there were 11 in 2006.
Typically, when a player hits 40 home runs in a season, the player is a significant cut above the rest of the league offensively. In the 320 player-seasons in which 40 home runs were hit, 40-HR players owned a .429 wOBA and a 158 wRC+. In 2015, three out of the nine players to hit 40 home runs or more were significantly worse than what you might expect for a player with that kind of power.
Carlos Gonzalez (40 HR, .364 wOBA, 114 wRC+), Albert Pujols (40, .333, 116), and Nolan Arenado (42, .371, 119) all rank among having the worst 40-HR seasons of all time. By measurements of wOBA and wRC+, all three rank well within the fifth percentile among 40-HR seasons. Consider the following table of the 15 worst 40-homer seasons ever by wRC+.
|2000||Tony Batista||Blue Jays||41||100|
|1998||Jose Canseco||Blue Jays||46||110|
|2012||Adam Dunn||White Sox||41||115|
|1984||Tony Armas||Red Sox||43||119|
It probably shouldn't be much of a surprise that the Colorado Rockies show up on this list more times (6) than any other team (though note the absence of Larry Walker, who was not just a Coors Field product). This list really doesn't turn up many surprises - all players on this list either played in hitter-friendly home parks, at the height of the steroid era, or both. Seemingly the one exception is Tony Armas, but Fenway Park had a 110 park factor in 1984, and he hit a robust .268/.300/.513 while swatting those 43 long balls.
And then there's Tony Batista. Batista's career was seemingly dedicated to answering two questions: Can I stand perpendicular to home plate and still hit, and how many home runs can I hit and still be atrocious?
Batista hit 41 home runs and was precisely league average. Even at the height of the steroid era in a hitter-friendly ballpark, you almost have to be trying to be only average while hitting 41 home runs. But he did it by hitting .263/.307/.519, and on top of that he was an All-Star. This was the year that Carlos Delgado was flirting with the Triple Crown, so it's not like he made the team just so that the Blue Jays had a representative.
Not to be outdone, while playing for the Montreal Expos in 2004 Batista had the worst 30-home-run season of all time by wRC+. Batista hit 32 home runs while batting .241/.276/.455 en route to a 76 wRC+. That's horrendous for a player who got 650 plate appearances.
Revisiting these data and sorting now by wOBA we see the following table:
|2012||Adam Dunn||White Sox||41||0.346|
|2000||Tony Batista||Blue Jays||41||0.348|
|1998||Jose Canseco||Blue Jays||46||0.354|
|1984||Tony Armas||Red Sox||43||0.359|
|1963||Dick Stuart||Red Sox||42||0.366|
There's a lot of the same crew here, including all three of the 2015 seasons, although Pujols' campaign is now the worst. Pujols hit .247/.307/.480 in 2015. We also see a few new names - those of Dick Stuart, Juan Gonzalez, Rocky Colavito, and Sammy Sosa. This is a more diverse list (which I'm sure Vinny Castilla is happy to see) with a running theme of high power, low batting averages, and low on-base percentages.
The three historically bad 40-homer seasons in 2015 can't be called anything but an aberration at this point. Even the three poor seasons in 2015 don't take the mean wOBA or wRC+ greater than one standard deviation away from the historical means. Clusters are a perfectly natural statistical phenomenon and are the most likely explanation for this occurrence. It's just another one of those statistical blips on the radar that pop up throughout history.
Joe Vasile is a contributor at Beyond the Box Score. He is also the Broadcasting and Media Relations assistant for the Salem Red Sox, the Advanced-A affiliate of the Boston Red Sox. Follow him on Twitter at @JoeVasilePBP.