The Yankees (probably) shouldn't worry about Giancarlo Stanton's decline phase yet

We at Pinstripe Alley spend a lot of time defending Giancarlo Stanton, probably because the hate he gets relative to his production - 4.2 fWAR and a 127 wRC+ in 705 PA - isn’t really proportional. At the same time, even we have to admit that those numbers are a far cry from Stanton’s MVP 2017 season, and that they come with even more worrying peripheral numbers.

Commenter bkalish18 did a magnificent job of listing those numbers in a rebuttal to Tyler’s defense of Stanton a couple weeks back, so I’m just going to post an excerpt from that comment here.

The basic argument here, from what I gather, is that these statistical warning signs suggest that Stanton’s 2018 represents a new normal for him, and that should Stanton follow the average aging curve of his “phenom” cohorts, 2018 would represent the baseline from which he would begin his decline, which wouldn’t bode well for his return on investment numbers.

This is a much stronger argument than your run-of-the-mill “Stanton can’t handle New York, he’s a bum” takes, and as such it deserves a proper, in-depth rebuttal. This is what I will attempt to do here.

The first response I can make is that there’s no evidence that “phenoms” like Stanton have earlier peaks than non-phenoms. The Beyond the Box Score article that is referred to is probably - “Aging curves for phenoms”, posted by Henry Druschel on May 27, 2015 - actually makes the opposite point. Here’s a blockquote from the article, with emphasis added by me.

Indeed, it looks like my hypothesis that phenoms might have the physical traits of a 24-year-old at age-21 or -22 and would therefore stop improving sooner or decline earlier has no evidence to back it up. Again, there is substantial volatility in the phenom curve, so it’s best to focus on the general trend rather than individual data points (like the inexplicable decline for phenoms at 26 and 27), but it seems clear that in these samples, the phenoms have a longer plateau than the non-phenoms. Their WAR/600 doesn’t begin to decline until their age-29 season, as opposed to age-27 for the non-phenoms, and their wRC+ stays almost at peak from age-25 through age-31, compared to the single-year peak at age-26 for the non-phenoms. It appears that not only are these players great earlier than their peers, they remain great longer than their peers.

So much for the argument that Stanton is approaching the dangerous part of the aging curve. Of course, that becomes a moot point if Stanton’s ostensible decline in several key peripheral stats holds steady going forward. However, I will argue that there just isn’t enough evidence to declare that those stats represent a trend, rather than fluctuations within the range of Stanton’s past outcomes.

There are a number of trends to monitor regarding Stanton. These can be divided into two main categories - plate discipline stats (BB and K rates, O-Swing%, and Contact%) and batted ball stats (ISO, FB%). A cursory glance at Stanton’s career reveals that those numbers have jumped around quite a bit over the years.

Here’s a graph of his yearly BB and K rates and O-Swing%:

FanGraphs.com

And here’s his contact rate:

FanGraphs.com

In one sense, there is certainly reason to be worried, as Stanton has fared worse in all four of these metrics compared to last year. Looking at the bigger picture, though, these graphs suggest that Stanton’s 2018 plate discipline numbers are more or less within the highs and lows of his career. A deviation from career norms would certainly be cause for concern. From the looks of it, this isn't it.

Now let’s do the same for Stanton’s batted ball stats. First, his ISO:

FanGraphs.com

Compared to Stanton’s plate discipline stats, the decline from 2017 to 2018 is indeed sharper and more alarming. Yet the same could be said for his 2015-2016, or 2012-2013. All this graph can conclusively tell us is that Stanton’s ISO has jumped around quite a bit. This is nothing out of the ordinary, as ISO correlates strongly with HR/FB, a notoriously fluky stat.

FanGraphs.com

More concerning is the trajectory of Stanton’s FB%, as shown below:

FanGraphs.com

Stanton’s FB% did deviate from career norms in 2018, as his 36.6% mark represents a new career low for him by nearly two percentage points. Now, for normal players a higher fly ball rate doesn’t necessarily lead to better results, but for sluggers with prodigious power like Stanton, consistently hitting the ball in the air is key to maintaining high production levels. It would certainly be nice to see Stanton approach a FB% closer to 40%. In this regard, recent trends have been more encouraging.

FanGraphs.com

After a mid-season crash, Stanton’s FB% has recovered to at or above his career norms. One would like for him to avoid such prolonged crashes in the future. In the meantime, though, there’s little here to suggest Stanton is losing the ability to consistently generate fly balls.

Overall, while all of the “warning flags” in Stanton’s profile do represent drop-offs from last year, none of them, save for his FB%, represent a deviation from career norms. Even for his declining FB%, more granular trends suggest that nothing’s really out of whack. That, combined with there being no evidence on “phenoms” having earlier aging curves than normal players, should be evidence enough to keep Yankee fans from being overly apprehensive about Stanton’s future performance. It’s all right to be disappointed in Stanton’s 2018 if you were expecting an MVP-like performance. You just might get one next year, or the year after that.