Number 1: Andrew Miller
| Pitcher | ERA | FIP- | WHIP | IP | K% | BB% | WPA/LI | fWAR |
| Andrew Miller age 28-30 | 2.15 | 52 | 0.94 | 154.2 | 40.3 | 8.7 | 3.52 | 4.6 |
| Craig Kimbrel age 28-30 | 2.44 | 57 | 0.91 | 184.1 | 42.3 | 10.4 | 5.14 | 6.0 |
| Difference in Performance (Kimbrel – Dotel) | +0.29 | +5 | -0.03 | +29.9 | +2.0 | +1.7 | +1.62 | +1.4 |
| Andrew Miller age 31-33 | 2.00 | 49 | 0.88 | 171 | 39.1 | 6.8 | 5.15 | 5.7 |
And Kimbrel’s closest neighbor is perhaps the only pitcher who can match Dirty Craig strikeout for strikeout. Andrew Miller and Kimbrel account for two of only three relievers in MLB history to strike out more than 40% of batters in their age 28-30 seasons in at least 150 innings of work (the other is Dellin Betances).
Miller was, of course, a Red Sox himself once upon a time. A post-hype prospect, Boston acquired Miller in 2011 as a reclamation project and revitalized his career before trading him for Eduardo Rodriguez in 2014. Miller didn’t fully find his footing until his late 20’s but once he did he became flat-out unhittable. His rate stats above mirror Kimbrel’s almost perfectly and, judging by his performance after he turned 31, that’s not bad news.
Miller would only become more dominant during 2016 and 2017. Over those two seasons, his ERA+ was 311 and striking out 14.3 per nine while allowing only 2 walks and 4.8 hits per nine. Last season didn’t go as well for the southpaw. Miller battled shoulder injuries all year in 2018 and greatly underperformed expectations, but if the Red Sox had signed Miller to a 5-year $85 million dollar deal before 2016 and things had played out the same for him it’s hard to believe anyone would be complaining right now.
So there you have it. This exercise has not given us a concrete idea of what to expect from Craig Kimbrel in the near future. He probably won’t blow up like Dotel and he probably won’t be historically great like Miller and Nathan. But it has given us a range of possible outcomes based on historical precedent.
The results of this analysis appear to make sense. It seems like a reasonable distribution of results to say that 1/5th of the time a Kimbrel contract looks like a disaster, 2/5ths of the time it becomes a slight overpay, and 2/5ths of the time he’s worth every penny. If that’s about right then the next question is this: Should the Red Sox make that gamble? With the current free-agent market for relievers and the dearth of prospects that the Sox can trade for a backend bullpen piece, I’d say it definitely is.