Nelson Cruz and Aging Curves

Nelson Cruz became the most recent member of the 400 home run club when, on September 22nd of last year, he hit his penultimate home run of the season. Reaching 400 home runs is special for a number of reasons. First, 400 is a large, and round, number. Second, home runs are (surprise!) high value hits. Less facetiously though, 400 home runs is particularly exciting because Nelson Cruz took a unique path to surpass that threshold.

Cruz had a brief cup of coffee with the Brewers in 2005; in 2006 though, Cruz was a member of the Brewers AAA affiliate Nashville Sounds when he was included as part of the Carlos Lee deal, which sent him to the Rangers. 

But a change of scenery didn’t immediately launch his career. Cruz played exclusively with the Rangers in 2006 following that trade, but struggled and found himself splitting time between AAA and MLB in 2007. His AAA/MLB splits, in tandem with his relatively advanced age, sometimes earned him the pejorative classification of Quadruple-A ballplayer. Ahead of the 2008 season, Cruz was exposed to, and passed unclaimed through, waivers. After being reassigned to the minors though, he continued to rake in AAA, but more meaningfully for his career, he finally replicated that production in a full month with the Rangers to close out 2008.

Since the beginning of 2009, Cruz has reeled off 11 straight 20+ home run seasons, four of which were of the 40+ variety. There were newsworthy storylines along the way too. He raked his way to the nickname Boomstick in the Rangers. He also earned an ALCS MVP for, among other things, hitting 6 home runs in 6 games of the 2011 ALCS. Days later, he couldn’t quite reach a now-infamous triple off the bat of David Freese. Cruz was later a key name in the Biogenesis scandal. He is a prime, and maybe the first, example of what can go wrong for a player the year after rejecting a qualifying offer. 

His slow start, which gave way to proficient production, left Cruz in strange territory as he eclipsed the 400 home run mark. Below is a scatter plot which illustrates that territory; all 400 Club members (of which there are 57) are included. Their home run totals from before their age-30 season are represented along the x-axis while their home runs on and after their age-30 seasons are on the vertical axis.

As we can see, Cruz is in a realm of his own. That is because just 77 of his 401 career home runs came before his age-30 season, leaving him with a more lopsided ratio than everyone else in the 400+ home run cohort.

To put Cruz into more concrete context, below are two tables. The first offers some summary statistics for the post-30 home run ratio leaders. The second is an identical table but sorted by the pre-30 home run ratio leaders. These tables give a clearer picture of which players did their heavy lifting before, or after, their age-30 seasons.

Already, Cruz is the runaway leader in the first leaderboard. No one else is particularly close given that Cruz hit more than four-fifths of his home runs after 30, and this percentage will only continue to grow in 2020. On the other end of the spectrum, one can either appreciate the incredible start to Andrew Jones’ career or lament how abruptly it came to an end. 

One final illustration highlights both the irregularity and consistency of Cruz, however. Below is the running total of Nelson Cruz’s home run count. 

When I think of climbing home run totals, I (wisely or not) tend to picture some form of an S-Curve, possibly representing the modest start of a player’s career, followed by the acceleration of their peak, and finally the evening out which represents their decline. The curve above does not conform to that anecdotal picture whatsoever. The Twins just exercised the option on their deal with Cruz for 2020 and, despite his age, his decline to this point appears nowhere in sight.