The 2015 Boston Red Sox had many problems, and one of those was the bullpen. Although the team had (and still has) Koji Uehara and Junichi Tazawa, the lack of depth in the pen hurt the team. Ian York takes a look at the repertoire and results of closer Craig Kimbrel to see what the Red Sox acquired.
When the Red Sox traded for Craig Kimbrel, they acquired one of the best, if not the best, relief pitchers in baseball. Kimbrel has led the National League in saves for four of his six years in the majors, and his numbers show that he has earned those saves; his career WHIP (0.927), strikeouts per nine innings (14.5), and strikeouts/walk ratio (4.33) are all elite.
Kimbrel throws only two pitch types, a four-seam fastball (abbreviated “FF”) and a curve (which PITCHf/x identifies as a “knuckle curve”, “KC”). (A couple of other pitch types, including changeups and sliders, have been identified by PITCHf/x algorithms, but since there are fewer than a dozen of these other pitches among the nearly 6000 Kimbrel has thrown, they are most likely mis-labelled.) Over his career, Kimbrel has thrown a fairly consistent mix of about 70-75% fastballs and 25-30% curves, regardless of batter-handedness:
Both pitches are outstanding. Kimbrel’s fastball averages over 97 mph, third among all pitchers in baseball in 2015 (50 innings or more), and his curve, at 86.8 mph, is second-fastest (pooling FanGraph’s CU and KC leaderboard), about 10 mph faster than a typical curve. What’s more, Kimbrel’s curve has excellent movement for such a fast pitch, averaging over ten inches of break. Here are average curve (and knuckle curve) speed and break for all 2015 pitchers, with Kimbrel’s shown in red:
Most of the movement on both his fastball and his change is vertical; his fastball has significant rise (relative to the path it would take in the absence of spin), and his curve has dramatic drop. Here are a pair of pitches that are close to Kimbrel’s averages in terms of velocity, location, and movement. The fastball was thrown to Tony Cruz, in the 9th inning of the game on August 23, and was fouled off; the curve was to Trevor Brown in the 9th inning on September 23, and was taken for a ball.
Even though the two pitches follow almost exactly the same path for the first 30 feet or so, in the last tenth of a second the pitches pull apart vertically (look at the “side view”), ending up a full 18 inches apart.
Kimbrel has racked up elite closer numbers for four of the past five years, but last year he was merely very, very good. His ERA+ of 142 was by far the lowest of his career, and his OPS-against of .569 was a full .100 points higher than his career average. Is it possible that he is on the downside of his career already?
His numbers really show no signs of decline. First, while he has thrown a lot of high-leverage innings since his debut, he is just 11th among relievers in that period for pitches thrown, with about 5900, and is well behind the leaders (Tyler Clippard has thrown over 8000 pitches in the same time).
His pitches show no signs of losing velocity or movement since his debut:
If there is any change from previous years to 2015, it is that Kimbrel’s curve averages a little faster; not because he is throwing most of them significantly harder, but because he is more consistent in his velocity, no longer throwing a set of slightly slower curves with slightly more movement.
There is also little difference in his location. This chart shows his pitch distribution each year since 2010. These are shown from the umpire’s viewpoint, so that batters would be standing in between the charts. The grey polygon in each plot shows the strike zone, as umpires were calling it that year:
Kimbrel tends to throw his fastball in the strike zone, though he does an excellent job of targeting the top and sides of the zone. His curves typically drop out the bottom of the zone, but enough stay at or above the bottom of the zone that batters can’t simply ignore them. In 2015, a slightly higher percent of curves were just below the zone, but the pattern was very similar.
In general, then, there are no signs that Kimbrel’s pitches are declining, and when we look at Kimbrel’s 2015 in more detail, the red flags become, at worse, a light pink. Most of Kimbrel’s relatively bad numbers came down to a handful of games at the beginning of the season. We can look at his WHIP and earned-runs per inning pitched as rolling ten-game averages, with his season averages shown as horizontal lines:
After a peak in May, Kimbrel’s numbers rapidly improved and then stabilized throughout the year. In the second half of 2015, his OPS-against was down to .426 (compared to his first-half .675), much more in line with his career numbers.
Kimbrel is not only one of the best closers in baseball, he is one of the very few who has shown consistency in the role, and at 27 years old, with a very reasonable pitching load, he has the potential to continue as an elite closer for years to come. No closer is a sure bet, but Kimbrel is as sure a bet as any.