Joe Nathan, Tiger For Two Years

No team gave up as many runs in the seventh inning or later last postseason, and so one offseason goal was clear for the Tigers: improve the bullpen. So the Tigers started at the back end of the bullpen and are finalizing the details for a two-year contract with Joe Nathan. They had the money because of recent cost-saving measures, and they had the need, and the contract isn’t long. What’s the prognosis for Nathan over the next two years?

Maybe the risk is no worse than you would have with any other established 39-year-old reliever, which is to say, a ton. Check out the aging curve for relievers thanks to Bill Petti and Jeff Zimmerman. Yikes.

But Nathan was good last year and all aging is relative. So he’s dropping off a good baseline and has room to be worse and yet still what the Tigers, and your fantasy team, need. One thing you’ll notice from that research is that velocity is more important to relievers than to starters. That’s probably because relievers have fewer pitches. If you look at Joe Nathan’s seasonal averages, you’ll see that he had his slowest fastball of his career last season. But zoom in a little further, and things look a little different:

To some extent, seasonal variation is to be expected. Velocities peak in August overall, and that’s what you see with his seasonal work. But, even beyond that, you can see some ‘shaking the rust off’ in Nathan’s velocity readings. For example, look at his first season back from Tommy John. He was down big, then he took some time off because of scar tissue working itself loose, and then, by the end of the season, he was more vintage Nathan. In 2012, he was that Nathan all year. Last year, he averaged 93.2 mph on the fastball from May first to the end of the season. He was excellent in 2008 and 2009 with that kind of velocity.

Maybe there are fewer miles on Nathan’s arm than your typical late-thirties reliever. He was converted to pitching after college, by the Giants, and then to relief fairly quickly. His elbow ligament is fresh, but there is some worry — research by Jeff Zimmerman suggests that there’s a 400-inning ‘honeymoon’ between your first and second Tommy John surgeries, if you are destined to have a second. By making it a two-year deal, the Tigers are staying out of the dangerous part of that honeymoon — the part where the groom sneaks away to check on his fantasy team — and you should probably have less confidence in him with every passing year, too.

But yeah, there’s risk here. Since Nathan’s only plus secondary pitch is a slider, he relies on his fastball for whiffs too. Right now, at 93+, he gets 12% whiffs on the fastball, which is almost twice as much as your typical four-seamer. But back in early 2011, when he was averaging just over 92? He got 9% whiffs on his fastball. That’s the year when he didn’t strike out a batter per inning and gave up all those homers…