On the podcast last week I gave my regression candidate as Jordan Zimmermann, but after looking further into the numbers I may have been wrong, but I also may have been right. Jordan Zimmermann has only made 81 starts and pitched 479 1/3 innings. There is barely a mean to regress to. The biggest worry with Zimmermann is that while he had a 2.94 ERA he also had a 3.51 FIP, but his K/9, BB/9, and HR/9 were all relatively in line with his career averages. In 2012 Jordan Zimmermann had a K/9 of 7.04 compared to a career average of 7.44, a BB/9 of 1.98 to 2.12, and a HR/9 of 0.83 to 0.90. This data is scaled towards Zimmermann's 2012 season possibly because his 195 2/3 innings pitched in 2012 is 40.8% of his career innings.
Looking at all that and figuring if Jordan Zimmermann pitches in 2013 like he did in 2012 then he should regress slightly from an ERA of 2.94 to something closer to either his 3.51 FIP or his career ERA of 3.47. Zimmermann in his career has been around a 3.50 ERA pitcher which is still a very good pitcher, but not as good as a 2.94 ERA pitcher. There are other facts to consider though. 2012 was the first time Jordan Zimmermann pitched a full season and if he remains healthy in 2013 it should become the season in which he first eclipses 200 innings.
Up until now the term regression has been used as a negative one, but look at Jordan Zimmermann's 2012 broken down by month. In total in 2012 batters hit .251/.297/.388 off of Zimmermann. When Jordan Zimmermann got to August and September something changed. This was the furthest Zimmermann had pitched into a season and suddenly batters hit .290/.350/.449 in August and .265/.333/.456 in September. It was the deepest that Zimmermann had pitched into a season and in those uncharted waters Zimmermann was at his worst. His ERA jumped to 4.39 and 4.41 in those last two months and a pitcher that for the season averaged just over six innings pitched was averaged around five and a half.
If we remove those last two months from the rest of Zimmermann's season then the difference is even more shocking. Zimmermann in his 21 starts before August averaged 6 1/3 innings and had an ERA of 2.28. Once August hit Zimmermann wasn't going as deep into games and wasn't pitching as effectively. There is evidence to suggest that Jordan Zimmermann ran out of gas. Combine all this with the fact that there isn't a real mean for Jordan Zimmermann to regress to and perhaps his mean is the numbers he was putting up before August of 2012.
Until Jordan Zimmermann has more data points in his career, there simply isn't a large enough sample to say what his mean is, but with the evidence that he ran out of gas near the end of 2012 and with that year of experience under his belt Nationals fans may be wise to not expect Zimmermann to perform worse, but perhaps to expect him to perform better. Zimmermann has other flaws. For his career Zimmermann has pitched significantly worse in the later innings than he has getting there. Zimmermann also can be too aggressive in the strike zone when ahead in the count and give up a couple hits that could have been avoided. A lot of this stems from that fact that Zimmermann doesn't have a true third pitch, but that is something that can be developed. Zimmermann is still growing and developing as a pitcher. 2013 will be a very interesting year to watch in the development of Jordan Zimmermann and there is evidence to suggest that his regression won't be to the negative side but instead to the positive.