Signing Miguel Castro was a good move.
He has elite velocity (98.0 MPH sinker) and an elite secondary pitch (slider). It is elite because it has 10.3 inches horizontal break. As you might expect, it gets a high rate of whiffs (.159 whiffs per pitch to right-handed batters and .139 whiffs per pitch to left-handed batters).
In December, the Diamondback signed him because he was the type of player they needed in the bullpen, and with the expectation that he could improve. Three things that Mike Hazen mentioned were better use of his sinker, increased use of his slider to left-handed batters, and more consistent location of his pitches.
He did improve! This season, there was an unbelievable improvement in his sinker, as measured by wOBA (35% better), by SLG (39% better), and by hard hit percent (33% better). Also, he improved his slider use against left-handed batters (66% increase in frequency). There may be other measures, but 18% reduction in walks per-batter-faced is one measure that shows he improved his consistency of pitch location. The following table shows that Miguel Castro improved in the three areas that Mike Hazen mentioned.
Baseball Savant’s Statcast data shows that by several measures, Miguel Castro is close to a career best season.
- 28.3% Hard Hit Percent (career best)
- 9.4% Bases-on-Balls Percent (second best season, 2016 was best with 7.5%)
- .289 wOBA (within .003 of career best)
- 3.95 Expected earned runs average (xERA) (within 0.16 of career best)
Although his xERA and whiff percentage are only above average, several other measures indicate that Miguel Castro is among the best pitchers in the Majors.
- 97th percentile hard hit percent
- 93rd percentile exit velocity
- 77th percentile barrels
- 91st percentile fastball velocity
What do my favorite metrics for bullpen pitchers show?
There are some measures that tend to show Miguel Castro results have declined in the last two seasons. Those measure include my favorite bullpen metrics. However, the whiffs per pitch and BIP per strike measures failed to capture his unique strengths because:
- .159 whiffs per pitch for sliders to RHB
- .139 whiffs per pitch for sliders to LHB
- .248 BABIP is much better than the league average of .295 BABIP (fewer balls-in-play are hits because his low average exit velocity and low hard hit percent.)
Although the following table falls short of fully capturing Miguel Castro’s strengths, it was included because it is my standard way of looking at bullpen pitchers.
This season Miguel Castro was elite against right-handed batters.
The following table shows his split. The important measures that show how good he is against right-handed batters are walks, OBP, slugging, and sOPS+(which compared him favorably to other pitchers in the Majors). This season against right-handed batters, his OBP and SLG were better than the league averages of .318 and .415.
What happened when batters hit ground balls?
Perhaps the clearest way to see that Miguel Castro improved is look at batters’ results when they hit ground balls. Baseball References hit trajectory split shows two things:
- Miguel Castro is better than average for grounders, fly balls, and line drives
- His sOPS+ of 18 on ground balls is truly elite.
See the following table for details.
What were this season’s results in high leverage games?
The following table shows the percentage of high leverage appearances (leverage at least 20% more than average) with no earned runs allowed. It shows a excellent results except in June and August.
What inning is Miguel Castro’s best?
The following table shows his results are best in the sixth inning and second best in the seventh inning.
Usually leverage is lower earlier in the game. Therefore the question is whether Miguel pitched better in the sixth or seventh inning because he was comfortable in that role or because the leverage was lower. Whichever is the answer, it explains why he sometimes closed early in the season but moved to other roles later in the season.
Miguel Castro was an excellent addition to the bullpen. He is having a career best season and his strengths are among the best in the Majors. He is an elite pitcher against right-handed batters. He is an elite pitcher when batters hit ground balls. He is at his best pitching in the sixth or seventh inning.