The source behind Kevin Siegrist's 2015 success: Increased changeup use

Last season, St. Louis Cardinals left-handed relief pitcher Kevin Siegrist threw a grand total of 24 changeups (down from the 50 he threw in 2013), as compared to 494 fourseam fastballs, 31 sliders, and 16 curveballs (per BrooksBaseball). As you may recall, over the offseason, I tried to figure out why Siegrist was ineffective in 2014 (4.62 FIP, -0.2 fWAR), but I was unable to find a concrete reason because there were seemingly indistinguishable differences between his 2013 and 2014 processes. As a cop out, I brought up the term "reliever volatility" as a possible explanation. Well, 53.2 innings into 2015, Siegrist, by fWAR (1.2), has outperformed 24 qualified starting pitchers—including (big) names like James Shields (1.1 in 152.2 IP) and Alfredo Simon (1.1 in 123.1 IP). As a reference, here is Siegrist's current stat line:

In terms of fWAR, the only Cardinals reliever Siegrist trails is Trevor Rosenthal (1.8), and as I discussed yesterday, that's okay because Rosenthal is the team's best reliever. Compared to 2014, Siegrist's HR/FB rate has predictably plummeted from 12.0% to 5.0%, but the most promising improvement is his walk rate, which has seen a 23.5% decrease from last season and is down even further from his superb 2013 season (when it was 11.8%). Let's get into the main point of this article, though: his increased changeup use.

Changeup use

Given the flight of a left-handed changeup (down and in to LHH), it makes sense that Siegrist does not use the pitch against left-handed hitters, but I still found it interesting that he had not yet thrown a single changeup to a lefty until this season, where he has thrown a grand total of two (or 0.64%). Yet, if you look at Siegrist's usage pattern in 2015, it is reasonable to believe that a considerable portion of his 2015 success can be pinned on the increased use of his changeup.

With Randy Choate's delegation as the team's LOOGY, Siegrist's prolonged reverse platoon splits, and Mike Matheny's fondness of pronounced bullpen roles, Siegrist has been the primary set-up man in 2015, especially considering Jordan Walden has been unavailable since April. With set-up man as his "defined" role, Siegrist has faced 217 hitters so far this season, and 144 (66.4%) of them have been right-handed. Considering two out of every three hitters he faces are right-handed, it was a proactive decision by Siegrist to gain comfort with his changeup over the offseason. This comfort is abundantly clear because despite the Cardinals still having 49 regular season games left to play, Siegrist has already thrown 96 more changeups in 2015 than he did in 2013 and 2014 combined.

Changeup results

As tweeted by Ben Humphrey a few days ago, "it's hard to discern any pitch's value relative to a pitcher's other offerings" because "they're inextricably intertwined," but a stat line like the one seen in the table above, particularly the sub-.100 isolated power, is always positive, especially when it is related to a pitch used nearly 20% of the time.

A prime example of Siegrist's changeup effectiveness seen in last night's game

As first tweeted by J.J. Bailey of KMOV, Siegrist attacked Pirates Rookie of the Year candidate Jung Ho Kang with three straight changeups, going lower with each consecutive pitch. A closer look at the PITCHf/x data shows that each changeup was thrown slightly harder than the previous one: from 86.22 MPH to 87.18 MPH to 88.05 MPH. While the difference in these velocities was likely barely noticeable to Kang, the threat of one of these pitches being a 95+ MPH fourseamer led to the rookie looking foolish for three-pitch strikeout.

Bottom line

Different from posts I have written on changeups in the past, I barely discussed the details (i.e. pitch location, horizontal movement, vertical movement, etc.) of Siegrist's changeup. Why? Let me explain. Coming into 2015, the book on Siegrist was pretty short: expect a fourseam fastball 75+% of the time, and you can jump on it because you don't really have to worry about being off-balance on a "straight" offspeed pitch considering he throws his changeup only ~5% of the time. This is no longer the case in 2015. In fact, his changeup is a regular part of his repertoire against right-handed hitters, to the point where he can go an entire at-bat throwing changeups exclusively (see above).

As you have probably gathered by now, I am selfish when it comes to changeups, so there is something I would like to see from Siegrist in the years to come: increased changeups to left-handed hitters (under one circumstance). The problem with trying to introduce this mid-season is that it will be a delicate pitch given that many lefties crush pitches down and in. Thus, I envision Siegrist introducing a "backdoor" changeup of sorts—to use immediately following a 95+ MPH fastball on the inside corner. In the meantime, let's continue to enjoy the success he has had with the pitch against right-handed hitters.

Credit to BrooksBaseball and Fangraphs for data used in this post.