After a quick look at Marcell Ozuna’s stats, what you see depends on who you are. If you love the acquisition, you certainly notice the 142 wRC+—good for 15th in all of baseball—and the ISO of .237. Even a less sabermetrically inclined supported could point to his 37 home runs and 124 RBIs—third in the league—as a tremendous addition to the team.
There is, however, another side to this coin. Perhaps Ozuna had a career year in 2017. One that he will never replicate. Those in this camp can certainly point out his 2015 campaign, where the then 25 year old struggled. He posted a sub .260 average and despite playing fifty more games than in his rookie year in 2013, was a less valuable player overall.
The concern is not so much that Ozuna might regress at all, but that he might regress all the way to the mean. The idea that the Marlins sold high and Ozuna is truly the 106 wRC+ player from a year ago is a reasonable concern for the Cardinals. It is meaningful to consider the new Cardinal outfielder’s production within the context of an aging curve.
This graphic was put together by Jeff Sullivan at Fangraphs in 2013. What is noticeable, and perhaps troubling for the Cardinals, is that players don't improve after they make it to the Major League level. At least, that is what the data show for the last eight years. Their performance remains constant at first, and then starts to decrease around the age 26 season. Marcell Ozuna turned 27 in November.
Although this graph, and other similar data visualizations, are informative tools, they show group level data and don’t necessarily apply to the individual. For a second, though, let’s assume that this graph does apply to the individual and accurately predicts Ozuna’s value.
The outfielder is currently under contract with the Cardinals for 2018 and 2019. During his age 26 to 27 season, his wRC+ was 142. If, according to the graph, players in this group experience a decrease in value of around six points, Ozuna will still be extremely productive this year. Even in the 2019 season, again following the graph, he is projected to have a wRC+ above 120. With typical regression, Ozuna is still a valuable player.
After a bit of research, and an admittedly small sample size, players who produced a wRC+ value between 140 and 145 have, overall, gone on to continued success. From 2013 to 2016 thirteen players had values in this range. Of those, only one player’s production dropped below 100 wRC+ the following year: Jayson Werth, who was going into his age 35 season—a full eight years older than Ozuna. Five of the thirteen players produced a wRC+ between 100 and 120 the next season, but seven of the thirteen produced a wRC+ above 130.
This trend is likely due to talent. A player who is able to maintain a wRC+ value like Ozuna produced in 2017 is clearly greatly skilled. Consequently, producing one season of that caliber is probably not a fluke. Even still, Ozuna has now produced two seasons with wRC+ values of at least 116 with WAR values of 3.9 and 4.8.
The data conclusively show that regression for Ozuna is likely, but that decrease in value is not so significant that it takes away his elite label. Realistically, he may never replicate or improve upon his 2017 performance. What remains, however, is a skilled player with tremendous value.