First, Iwakuma doesn’t have overwhelming fastball velocity, as he has consistently averaged around 90 mph. Furthermore, Iwakuma has displayed a broad pitch repertoire. According to BrooksBaseball, Iwakuma throws a fastball, sinker, slider, curve, splitter, and added a cutter this year. He has primarily leaned on his splitter this year, and it has been dominant, drawing nearly 20% whiffs.
As we dig deeper, we can see that some of Iwakuma’s success can be attributed to a high groundball rate – his GB% of 49.8% is well above the league average of 45%. This helps him limit home runs, which keeps his ERA down.
Iwakuma has consistently allowed a low BABIP. Studies have shown that pitchers do not have much control over their BABIP, so a consistently low BABIP seems a little suspect.
Additionally, Iwakuma has benefited from a very high strand rate (Left On Base Percentage, or LOB%) during his first two seasons here. Pitchers have very little control over their strand rate, and most extreme strand rates result in a regression to the mean during the next season. During Iwakuma’s first two years in the MLB, he had not seen this correction.
At the start of 2014, Iwakuma seemed to be the same pitcher he was before, and had all the same characteristics. Through the first half of the season, his strand rate was at 79.7%, which is well above the league average. However, in September, Iwakuma faced extreme regression, and his strand rate collapsed to 51.8%. His performance suffered as well, as his BABIP increased to .371 and his ERA for September and October climbed to 7.61.
In an effort to answer some of these questions, I looked at pitcher comparisons for Iwakuma. I tried to find pitchers that fit some of Iwakuma’s key characteristics:
· High strand rate for three consecutive seasons
· Low BABIP for three consecutive seasons
· Above average GB%
· Low fastball velocity
· Non-elite strikeout numbers (<8 K/9)
Looking at data from 2002-2014, I ended up finding six pitchers who seemed like the best comparisons for Iwakuma. While none of them were perfect matches, their career trends may provide insight on what we can expect from Iwakuma in future seasons. It is important to note that we are clearly dealing with a small sample size. Six pitchers is not nearly enough to draw definitive conclusions, but it may give us an idea for what we can expect from Iwakuma going forward.
Each player has a comparison to Iwakuma’s 2012-2013 data.
His BABIP remained low in subsequent seasons, so he was able to maintain success despite strand rate regression.
All statistics used are from FanGraphs.