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Has Age Caught Up to Joe Nathan?

Tigers closer Joe Nathan once again finds himself in a desirable fantasy situation. By moving from Texas to Detroit, Nathan gets to close for another contending club. Nathan is also coming off one of the finest seasons of his career. Over 64.2 innings, Nathan posted a 1.39 ERA with 43 saves. In most cases, fantasy owners would be comfortable relying on that closer the following year. In Nathan’s case, his age is starting to get worrisome. Nathan will be 39 when the season begins, and he’ll need to defy Father Time if he wants to continue posting excellent numbers.

Even before looking at his age, one can see signs of decline in Nathan’s 2013 numbers. For one, it’s impossible to expect any pitcher to repeat a 1.39 ERA again. Nathan’s 2.26 FIP was pretty excellent, so there’s no real need to complain there, but don’t go into this expecting a sub-2.00 ERA again. Part of the reason for that will be Nathan’s home run rate. Last season, he posted an all-time low 3.0 HR/FB rate. Nathan’s career figure in the category hovers around 7.0%, so he’s due to see some decline in that area, despite moving to a stronger park. Even with those numbers evening out next season, Nathan’s numbers should be good enough to use moving forward.

That’s where his age comes in. Eno Sarris chronicled some of the issues Nathan will face in a December article. Using Bill Petti and Jeff Zimmerman‘s pitcher aging curves, it’s pretty evident that most relievers tail off in a big way around age-37 or age-38. Eno hedged on that somewhat, by saying Nathan’s velocity was actually fairly strong despite his age last season, offering hope he could continue to remain effective despite some risk.

At the same time, there’s likely a reason Petti and Zimmerman did not chart pitchers past age-38. The sample was probably quite small, indicating few pitchers are actually effective at the same age as Nathan. But you could argue that the pitchers who remained effective in their late-30s were good enough to continue posting strong numbers for a few more years. While Nathan is no Mariano Rivera, that’s essential what Rivera did over his career. In order to see whether this is the case, we can look at how similar pitchers performed at age-39.

Name SV IP K/9 BB/9 ERA FIP xFIP WAR
Mariano Rivera 69 142.0 9.57 1.14 2.28 2.34 2.60 5.4
Dennis Eckersley 87 147.0 10.59 1.47 2.94 2.14 4.8
Larry Andersen 20 142.2 8.39 2.52 1.96 2.02 4.4
Joe Nathan 80 129.0 10.53 2.44 2.09 2.52 2.94 4.2
Koji Uehara 22 110.1 11.75 0.98 1.31 1.87 2.27 4.2
Takashi Saito 57 111.1 11.16 2.34 1.86 2.33 2.77 3.5
Todd Jones 77 137.0 5.91 1.64 2.96 3.01 3.65 3.3

The above chart shows the seven relief pitchers who have posted at least 3 WAR over their age-37 and age-38 seasons since 1969. The talent on the list mostly speaks for itself. Rivera and Eckersley are Hall of Fame talent. Uehara and Saito were both effective at advanced ages. Andersen posted some strong numbers despite seeing few save opportunities over his career. Jones is the one guy on the list who really stands out as a strange choice. The point is, most of these players had successful careers, just like Nathan. So, did those strong numbers repeat at age-39?

Name SV IP K/9 BB/9 ERA FIP xFIP WAR
Mariano Rivera 44 66.1 9.77 1.63 1.76 2.89 2.42 2.0
Dennis Eckersley 19 44.1 9.54 2.64 4.26 3.42 0.9
Todd Jones 38 61.1 4.84 3.38 4.26 3.92 4.66 0.9
Larry Andersen 2 35.0 9.00 2.06 3.34 2.30 0.8
Takashi Saito 2 55.2 8.41 4.04 2.43 4.25 4.78 0.5

The above chart shows how these pitchers performed at age-39. Rivera once again posted an excellent year. The other four players on the list all saw some decent decline. Eckersley and Jones saw their ERAs shoot above 4.00. Anderson was still somewhat effective, but didn’t pitch as much. Saito finished with a strong ERA, but his skill had eroded. His 4.25 ERA is more indicative of how he pitched. Admittedly, it’s a small sample, but that’s to be expected when dealing with 39-year-old pitchers.

What does it mean for Nathan? Mostly that his age is a legitimate issue. Few pitchers are capable of putting up strong numbers once they are in their late-30s. It’s tough to bet against Nathan next season, considering his situation and last year’s numbers. That combination will surely get Nathan drafted in most leagues. And while it would be foolish to completely stay away, fantasy owners should be well aware of the risks before taking the plunge on a 39-year-old.