Jeremy Pena’s Forgettable July and August

Jan 31, 2023 - 12:54 PM

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After Jeremy Pena’s MVP award in the World Series, the rookie shortstop became a star. Throughout the year, he was an excellent defender. But, what about his regular season offense? Two months were unlike the other four months.

Regular Season wRC+ and OBP By Month (wRC+ / OBP)

March/April 116 / .305

May 148 / .353

June 102 / .321

July 85 / .250

August 46 / .231

Sept./October 123 / .303

On the season, Jeremy Pena’s is basically around league average (wRC+ 102). However, without the two outlier months—July and August—the regular season wRC+ is 123 or 23% above league average offense. Pena’s offense seemingly hit bottom in August, followed by a strong Sept. / October. Since the rebound at the end of the season is followed by a great post season (wRC+ of 186 and OBP of .367), Astros fans are hoping that this represents a possible offensive breakout season for 2023.

On the other hand, one should be wary of extrapolating post season results to the regular season (Randy Arosarena says, Hello!). And though the results are higher, Pena’s post season peripherals (BB%, K%) are roughly the same as the regular season excluding July and August. Arguably, the post season offense is a continuation of September and October, and maybe also the early months of the season. Are June and July just normal volatility (albeit fairly extreme volatility)? Or should July and August be viewed as outliers which don’t represent Pena’s normal performance?

Baseball Savant’s Rolling xwOBA leaderboard “is intended to easily identify which players have turned around their performance.” Pena’s final 100 plate appearances are compared to the previous 100 plate appearances to determine the change in expected wOBA. Pena’s last 100 regular season plate appearances improved from .224 xwOBA to .348 xwOBA. This is the third best among all major league performers for the most recent 100 plate appearances. Only Yordan Alvarez and Glieber Torres ranked higher in improvement. This comparison largely shows the difference between Sept./Oct. and August.

July and August Performance

Let’s look more closely at July and August for answers.

• Pena returned from the injured list on June 29; he had suffered a thumb injury. Is it possible that he was still experiencing some effects from the injury? Or did the injury lead to some bad habits while batting?
• Ben Clemens at Fangraphs investigated the predictors of hitter breakout among power hitters roughly similar to Jeremy Pena and concluded that an improvement in contact rate is the best indicator of possible breakout. I don’t have monthly data for contact rate, but monthly K rate might be a reasonable substitute.
• The June/July K rate of 26.3% is higher than the 23.0% weighted average for the remainder of the year. The 21.5% K rate in Sept./Oct. is the lowest of the season.
• Pena hit mostly groundballs in June and July (51% and 57%, respectively) compared to 40% - 47% in the remaining months. There could be a number of explanations, ranging from continued thumb issues to the types of pitches he swung at. According to Baseball-Reference, Pena has a OPS+ of 69 against groundball pitchers.

September Swing Changes

As Pena struggled in August, he considered changes he could make in his swing. To some extent, Pena’s mechanical changes may have helped. This MLB Network video provides one theory about the change. In the midst of a Sept. 10 game against Shohei Ohtani, Pena eliminated his customary leg kick. In the video, Mark DeRosa suggests that Pena was frustrated with the large number of breaking pitches and decided to take a “two strike approach” without his leg kick. He had success and continued with that approach into the playoffs. DeRosa said he wouldn’t expect this to be a permanent change, but rather an approach he can take from time to time in order to get out of slumps.

Pena’s Walk Rates

Notice that my review hasn’t mentioned BB%. That’s because Pena’s walk rate didn’t vary much from month-to-month. Pena’s walk rate is uniformly low. Historically batters with a walk rate similar to Pena’s 3.9% do not fare well in the long term. Fortunately, rookies who enter the league with very low walk rates can and do improve with experience. The fact that Pena had higher walk rates in the minor leagues indicates that he has the capability to improve. Pena’s very low BB rate leads to offensive production which is too dependent on batting average on balls in play (BABIP). BABIP is notoriously volatile, which could explain the inconsistencies in July and August. Pena’s BABIP in July and August is 49 points lower than the average for the remaining months. A higher walk rate would leave Pena less vulnerable to on-base percentage slumps.

Kyle Ross-USA TODAY Sports

Conclusion

Obviously we can’t say with certaintly that Jeremy Pena’s offense will improve in 2023. The projection systems don’t forsee improvement. But reviewing his 2022 offensive output in context leads me to be more optimistic about 2023 offensive production. I think it’s reasonable to view his distressing July and August results as outliers. If you accept that premise, then it’s very feasible that Pena will achieve ZIPS’ 80 percentile offense, which produces a wRC+ of 115. As an Astros fan, I can hope for a more significant offensive breakthrough. Only time will tell.