When I first heard that the Tigers had signed Justin Upton, I'll confess that I felt rather lukewarm about the whole deal. Upton has long had a reputation as an incredibly talented player that has never taken the next step towards becoming a superstar, and frankly I harbored concerns over whether or not he'd be another dead contract in four years.
Well, the opt-out clause in his contract makes it a lot less likely that he'll even be in Detroit in four years. Even ignoring that caveat, however, it seems likely that he's going to be a more productive player in the medium to long term than his counterpart at the top of the outfield free agent market, Yoenis Cespedes.
The aging curve
The first and most obvious reason that Upton will be productive after Cespedes is their ages. Although Upton has been in the league for eight full seasons compared to Cespedes' four, the latter is already 30, while the former is just 28 years old. Considering Cespedes expects to get at least the same number of years, if not one more than Upton, the back end of their respective (projected) contracts already favors the Tigers.
It's also worth noting that Upton has had one of the most secure floors in the majors over the last five years. He hasn't posted a wRC+ under 109 since 2008 and has only been under 120 once in the last five seasons. Cespedes, on the other hand, has sandwiched two mediocre seasons (102 wRC+ in 2013, 109 wRC+ in 2014) between two great seasons (136 wRC+ as a rookie and 135 in 2015). A better understanding of those mediocre seasons? A drop on batting average on balls in play. While Cespedes makes very hard contact (almost 36 percent of the time in 2015!), he's still going to be hard-pressed to sustain a BABIP of .360 or greater in the long run. There's certainly the likelihood that 2015 was the best it'll ever get for him.
Upton has his own fluctuations in BABIP, but they tend not to affect his stock as much. This is because Detroit's new left fielder is much less of a free swinger. The difference between a 10.3 percent career walk rate and a 6.1 percent career walk rate may not seem like much, but it's a sustainable way for Upton to gain extra trips to first base. The disparity is growing recently, as well. Upton's last three walk rates have been 11.7 percent, 9.7 percent, and 11.0 percent, while Cespedes has steadily declined- 6.4 percent, 5.4 percent, 4.9 percent.
And that's maybe the single biggest reason that I lived in fear of the Tigers giving Cespedes a seven-year contract in recent weeks. He spent the first half of 2015 hacking more than anyone in the state of Michigan since Paul Bunyan. Swinging at 39.1 percent of pitches out of the strike zone may be okay when you're in the prime of your career and able to hit 60-65 percent of pitches outside the strike zone pretty much at will. But that skill goes away, and goes away fast! Josh Hamilton was once able to hit 60-65 percent of pitches outside the zone, but then he lost that ability and his contract became an albatross in no time. Fangraphs has a great read on how aging relates to plate discipline. What you have here is a clear case of two different styles of hitting on that age curve, and the Tigers bet on the one that is more likely to be successful down the road.
Of course, nobody can predict future success, and there's a strong likelihood that in 2021 both players are declining heavily (and most likely doing so for other teams -- thank you, opt-out). However, Upton is the player that stands the best chance in baseball's age-old battle against Father Time.