Chris Davis and Normalized Home Run Rates

Chris Davis hit his 51st home run of the season last night. 20 years ago, that would have been a pretty big deal, but the years around the turn of the century reset the bar for newsworthy home run totals. After having only two 60 homer seasons in the first 100+ years of baseball, we saw six such seasons in four years. 50 homer seasons used to be the stepping stone to greatness; now, Davis is still 22 home runs away from the single season record.

As we know, though, the game as its being played today doesn’t look like the game that was being played 15 years ago. The strike zone is bigger, the players are smaller, and both runs and home runs are much harder to come by these days. Chris Davis might not set any real records, but hitting 51 home runs (and counting) in this offensive context is still an accomplishment worth celebrating.

But rather than just leave it at that, we can actually just look at Davis’ home run rate relative to 2013 norms, and then compare that to other 50 HR seasons to see how Davis’ HR rate stacks up throughout recent history. So let’s do just that. In the following table, you’ll see each player who has hit 50 home runs in the 50 years preceding this one, with Davis’ 2013 season inserted into the mix, giving us 28 different 50 HR seasons to look at. I’ve also listed the ratio of plate appearances to home runs, the league average PA/HR ratio for that season, and then an index metric I’ve called HR+, that is simply a player’s PA/HR ratio divided by the league PA/HR ratio. Think of it as wRC+, just without the park adjustments, and for dingers only.

Not surprisingly, we see Bonds and McGwire at the top, but interestingly, look at how close Willie Mays was in 1965 to Bonds’ record 2001 season. While Bonds ended up with 21 home runs, a large part of that difference was just the league norms at the times in which they played. In fact, even Cecil Fielder’s somewhat forgotten 51 homer season in 1990 was not very far off the mark of Bonds’ HR rate once you adjust for league averages in that season.

And look where Davis stands. There’s four Mark McGwire seasons ahead of him, plus the Bonds/Mays/Fielder group, plus George Foster’s 1977 season, but Davis’ 2013 season stands ninth in normalized home run rate, well ahead of seasons with bigger HR totals. There’s no trophy for top 10 HR rate relative to league average over an arbitrary timeframe, but this is still an accomplishment worth noting.

But, while the last 50 years is a convenient timeframe for our leader boards, since they can display up to 50 seasons at one time, this window annoying excludes some of the more famous HR seasons in history. So, let’s see how the players in the previous 50 years to our sample did, giving us a range of 1914 to 1963. Prepare to laugh, or be amazed, or both.

Babe Ruth only hit 50 home runs in a season four times, but three of the four times he did it, the league average PA/HR rate was over 100, meaning that an average player in those years would hit five to seven home runs per year. In 1920, when Ruth hit 54 home runs, that accounted for 8.5% of the entire league’s total. These numbers just destroy what we’ve seen in the last 50 years, because the game was entirely different back then, with only a few players hitting balls out of the ballpark on a regular basis. The home run giants of that era towered over their competition in a way that no one does anymore.

Interestingly, look at where Maris’ HR+ rate lies in comparison to Cecil Fielder’s 1990 season. While there will always be some who attempt to proclaim Maris the “true HR champ”, since they prefer to invalidate all accomplishments during the “Steroids Era”, that argument is already along the path of adjusting for seasonal context. If we’re going to start down that path, might as well go all the way and acknowledge that Fielder’s 51 HR season was more impressive, given the difference in league average HR rates between 1961 and 1990. But, then, neither Fielder nor Maris can stack up to Ruth’s ridiculous accomplishments, given the norms of his day.

True home run champ? I’ll go with Barry Bonds, chemicals and all, given that he hit more home runs in a season than anyone else ever, and that’s really the answer to the question most people want to know. Most impressive HR hitter, relative to his own time? That’s Ruth, and it will be Ruth forever, barring some kind of weird changes to the rules involving pitchers throwing multiple balls at the hitter simultaneously.

Chris Davis isn’t in either of those conversations. And even with a huge barrage to end the year, he’s not going to end up in them. But, he’s playing in different environment than the one we saw 15 years ago, and what he’s accomplished is pretty remarkable. So kudos to Davis on his 51 homer (and counting) season, a feat that stands up pretty well against most of history’s best HR seasons.