What Should the Expectations Be for Andrew Miller in 2021?

Andrew Miller bounced back in 2020 after a difficult 2019 season which saw him allow a career high home run rate (1.81 HR/9) while also experiencing a drop of more than half a mile per hour from the previous season. However, Miller’s strong 2020 season (2.58 FIP, 3.20 K/BB) came with some serious red flags that make it unlikely that Miller will repeat his success in 2021.

To begin with, the St. Louis Cardinals’ reliever threw just 13 innings, thus giving him too small of a sample size to trust his results, especially after a 2019 season in which he was worth -0.4 fWAR. Additionally, the average velocity on Miller’s four seam fastball dropped below 90 miles per hour for the first time in his career. His registered average of 89.6 mph is nearly three miles per hour lower than his average fastball velocity in 2019 (92.4 mph).

It is certainly possible that this drop in velocity was just a blip. However, it is unlikely that the sample size played a part in his lower velocity, as he will also turn 36 years old during the 2021 season. Therefore, it seems unlikely that Miller’s average velocity will return to its previous levels.

Additionally, Miller did not allow a single home run last season, and his career high 58.1% groundball rate likely played a large role in this fact. However, the last time that the southpaw posted a groundball rate above 48% was in 2016. Thus, it seems that the small sample size played the largest role in his success at keeping the ball on the ground. When his groundball rate normalizes in 2021, his home run rate will surely rise.

Miller also dropped his walk rate by over 2%, giving him his lowest walk rate since 2017. Additionally, in 2020, Miller also posted his lowest zone percentage (47.8%) and lowest chase rate (22.4%) since 2015 (when Statcast data is available). Thus, it seems unlikely that his walk rate would not regress over the course of the full season unless he started inducing more hitters to chase his pitches.

Even though Andrew Miller had a strong season in 2020, it seems unlikely that he would have been able to maintain his success over the course of a full season. His decreasing ability to induce hitters to chase, as well as his decreasing velocity, and seemingly regression-bound groundball rate all make him unlikely to replicate this success in 2021.

Because of this, Mike Shildt and the Cardinals should not be relying on Andrew Miller as a high-leverage arm. Additionally, he may even be the least effective and least used of the three left handers that project to pitch out of the Cardinals’ bullpen.

However, this is not surprising. Both Genesis Cabrera (22 ¹⁄₃ IP) and Tyler Webb (21 ²⁄₃ IP) were used more than Miller last season. Cabrera is just 24 years old and has the arsenal of a power reliever who could rise into a high-leverage, late game role for the Cardinals while Webb is 30 years old (5 years younger than Miller) and has been consistently solid, if unspectacular, for the Cardinals.

Miller threw just 13 innings in 2020. However, he also dealt with shoulder fatigue that caused him to miss a series of games. Because of this, it seems that he did not approach the amount of innings that Webb and Cabrera threw, simply because of the need to rest his arm not because he was not trusted to pitch well. This is made even more clear by the fact that he recorded four saves in 2020. Clearly Mike Shildt trusted Miller to pitch in late game situations, but that should not be the case this season.

It is possible that the decrease in average fastball velocity is related to the arm fatigue that he suffered. If this is the case, then his fastball velocity will likely recover from last season, and he could have a solid season in 2021. However, if his fastball velocity does not recover, then it is unlikely that he will pitch as well as he did in 13 innings last year. Additionally, Miller is almost 36 years old, so his arm could be more prone to fatigue over the course of the season. Thus, it seems that trusting Miller in high leverage roles, instead of trusting some of the other young power arms that the Cardinals have in the ‘pen, could be a mistake.

If Andrew Miller is going to outperform any lefty, it will likely be Webb, but age appears to be catching up to the once dominant reliever. Thus, the Cardinals should not be expecting Miller to be anything more than a solid middle reliever, who sees more action against left-handed hitters. However, this is not a bad thing, because this could also be the year that Genesis Cabrera becomes the dominant left-handed reliever that can take over a high-leverage role. This would be a great development for the organization, and it would allow the team to not have to rely too much on a soon to be 36-year-old Andrew Miller.