The worst 40-homer seasons ever

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+.

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:

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.

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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.