Post DL stint, Trevor Rosenthal returned to form

Editor’s Note: This piece was originally published yesterday, but is being put back on the front page today given yesterday was a holiday and a lot of people were watching hockey at a baseball stadium. -CE

The 2016 season was a statistical and physical struggle for St. Louis Cardinals relief pitcher Trevor Rosenthal. After being the team’s primary closer for the previous two seasons — including setting the club record for saves in a season (48) just one year prior — Rosenthal was replaced in the role at the start of July by newcomer Seung Hwan Oh. And after sporadic, role-less use over the course of a month, Rosenthal was eventually placed on the disabled list with rotator cuff inflammation. Here is how Rosenthal performed prior to his placement on the disabled list:

Two statistics stand out in particular — BB% and BABIP. Both ballooned to rates in which Rosenthal had not yet experienced in his four-plus year MLB career. In fact, even after experiencing better batted ball luck upon return (see below), Rosenthal’s BABIP against (.425) remained the highest among relievers with at least 40 innings pitched last season. It wasn’t even close, either, as the second highest reliever (Edwin Diaz) ended the season at .377. Remember, the league average for relievers in 2016 was .296.

While there is no denying Rosenthal dealt with some rotten batted ball luck, the horrendous walk rate is entirely on him. Sure, he may have had seven strikes taken away from him by home plate umpires, but over the course of 738 pitches thrown, and a solid pitch framer in Yadier Molina, he gained 34 strikes as well. So, just as I said, the walk rate is entirely his problem. Again, even with improvement upon return from the DL, Rosenthal’s season walk rate (14.7%) ranked second highest among MLB relievers.

As we all know, Rosenthal returned from the disabled list in mid-September, with very few real updates about his condition along the way. Though Rosenthal had zero chance of reclaiming the closer role from Oh, his level of performance was admirable, especially when you review the same two statistics I discussed earlier. The walk rate dipped below his career rate and despite a still well above-average BABIP against, he still experienced positive results (ERA).

First and foremost, drawing a conclusion based off a sample size of seven innings pitched (or 30 batters faced) is not reliable. However, when you then take a closer look at the process — namely PitchF/x data (via BrooksBaseball.net and BaseballSavant.com) — as well, you cannot help but get excited about Rosenthal’s finish to the 2016 season.

Fourseamer velocity returned

Considering the starting point of the Y-axis, the spike in fourseamer velocity appears much more significant than it actually was. However, when his average fourseamer velocity is able to return to 98+ MPH, after dipping to a career low of 97.12 MPH in July, one cannot help but hope his health-related arm issues were successfully put behind him. The VEB community overwhelmingly agreed last offseason that Rosenthal possessed the staff’s best fourseamer, but this is only the case when he’s “all systems go,” as he appeared to be over his seven innings thrown in September and October. And no, Rosenthal’s “return” didn’t just stop with velocity, either.

More horizontal movement (recorded in inches) on the fourseamer

Remember, regarding horizontal movement in right-handed pitchers, a negative value means arm-side movement, whereas a positive value means glove-side movement.

Could this increase in horizontal movement be attributed to a significant change in horizontal release point? Potentially, but it was trending this way even in July and has jumped around throughout his career. Regardless, increased movement is a welcome development to a pitch that had seemingly “straightened out” in 2016.

Refined fourseamer location

Despite a smaller sample size (82 versus 582), Rosenthal’s fourseamer location was considerably more refined from September 16 through October 1 than it was from the beginning of the season through July 24. The point I am trying to make by bringing up the sample size disparity is that, theoretically, collecting more than one dark brown target (or what I call “core”) should be easier when dealing with a smaller sample size, as it takes fewer pitches to “achieve” a dark brown target.

Yet, as seen in the side-by-side comparison above, the heatmap with two “cores” is actually the one with the larger sample size. This shows us that Rosenthal was much more consistent with his fourseamer location after returning from the disabled list, though a deviation to the right — outside to righties and inside to lefties — would be even more desirable.

A solid pitch mix returned

As you can see, Rosenthal gained confidence in his secondary offerings upon return from the disabled list. I understand that I’ve spent the entirety of this post talking up his fourseamer — with good reason. Yet, in my opinion, this last point is probably the most important. Rosenthal has effective secondary pitches — particularly his changeup — he just seems to forget about them at times. With Oh primed to retain the closer role in 2017, Rosenthal will either be stretched out for a shot in the starting rotation or potentially be used in an Andrew Miller-type, multiple-inning role. A more developed pitch mix will only help in both scenarios.