How pitching and the usage of pitchers has changed in the postseason

With each additional year, the bullpen becomes evermore important to a team looking to win the World Series

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Present day managers rely more and more on their bullpens, especially during the postseason. The 2017 postseason has further perpetuated this trend.

The Usage of Pitchers

In the 33 postseason games in 2017, bullpens have already worked 265.1 of the possible 583 innings of work, or 45% of the available innings. In 2013, bullpens threw only 218.1 of the 655.2 innings in 38 games of postseason baseball, only 34.79% of all innings pitched. Ever since the Kansas City Royals appeared in the 2014 World Series with a bullpen army of Kelvin Herrera, Wade Davis, and Greg Holland (who are all closers now), the focus has shifted to shutting out those last three innings to, essentially, shorten the contest to a six-inning game for the home team.

Games in Postseason Innings Pitched by all Bullpen Total Innings Pitched in the Postseason % Innings Pitched by Bullpen
2013 38 233.1 670.2 34.79%
2014 32 239 595 40.17%
2015 36 258.2 655.1 39.47%
2016 35 272.1 629 43.26%
2017 33 265.1 583 45.51%

This approach has become most prevalent in elimination games. In both Wild Card games, the only pitcher who threw over three innings was Arizona Diamondbacks ace Zack Greinke, and he only lasted 3.2 innings. In Game 4 of the ALDS, the Boston Red Sox and the Houston Astros put in aces Chris Sale and Justin Verlander in the fourth and fifth innings, respectively. Gio Gonzalez and Kyle Hendricks threw only three and four innings of work in Game 5 of the NLDS.

The Changes in the Pitches Thrown

Pitchers have become harder to hit, mainly for one reason: increase in velocity. Over the past 15 years, the average velocity of fastballs throughout the league has steadily increased from 89 miles per hour to 92.8 miles per hour. A faster pitch is harder to hit because the hitter has less time to decide whether they should swing.

The variety of pitches thrown also affects hitters. Over the past 15 seasons, the pitchers have decreased the number of fastballs they throw by 8.8%. From the hitter’s perspective, having to hit a variety of pitches makes the job at the plate significantly harder. When a pitcher can capably throw at least one other pitch effectively, the hitter cannot fully commit to one pitch unless the count is in their favor.  Since those different pitches can be curveballs, sliders, or changeups, the movement or change of velocity also makes it harder to put the barrel on the ball.

So how do these numbers matter for making pitching decisions?

Managers want to take advantage of the increase in velocity and going to the bullpen arms is the easiest way to do this. Usually, relief pitchers only work for roughly one inning. For relievers, they do not have to concern themselves with stamina as much as starters do. When they take the mound, they can go all out for fewer pitches. This mindset is apparent in their average velocity numbers. This past season, the relief pitchers had an average fastball velocity of 93.8 miles-per-hour, a full mile-per-hour faster than the league average. In each year since 2002, the average fastball velocity of relief pitchers has been no less than 0.6 miles-per-hour faster than the league. Conversely, relievers throw less off-speed pitches. Since 2002, relievers have used at least 1.5% more fastballs than the league average. Evidently, managers have gone with more power arms when the game is on the line, and those power arms are in the bullpen.

The Pitchers Available from the Bullpen

With the shift in focus towards relief pitching, the best pitchers are now in the bullpen. Of the ten playoff teams, six of them ranked in the top six for bullpen ERA. Seven playoff teams occupied the top ten teams in bullpen FIP while six occupied the top ten in bullpen xFIP.

The reliance on these bullpens is not surprising. The Los Angeles Dodgers have relied heavily on Kenley Jansen (0.82 ERA, 0.55 WHIP) and Brandon Morrow (1.74 ERA, 0.58 WHIP) in the postseason. Apart from Jansen’s blown save in Game 2 on Wednesday against the Houston Astros, the two of them have been largely untouchable.

The New York Yankees relied on David Robertson (4.15 ERA, 1.15 WHIP), Tommy Kahnle (2.38 ERA, 0.71 WHIP), Chad Green (4.15 ERA, 1.04 WHIP) and Aroldis Chapman (1.13 ERA, 1.13 WHIP) to finish teams. While they might have some unusually high ERAs, this does not tell the whole story of how effective they were. Of the four, Robertson had the highest on-base percentage against, which was a still excellent .294 OBPA.

Possible Future Changes

This change in approach from managers has several implications on players within the game. For relief pitchers, each of them become more valuable the more frequently more teams use them. This also means that more average to below average starters might be more frequently turned into bullpen arms, where they can concentrate on fully attacking one inning per outing.

The focus of pitching could evolve even more. As starters become less and less valuable, especially in the playoffs, the idea of needing dominant starting pitching to win could become obsolete. One day, baseball could see a playoff staff that has a few pitchers working two or three innings, maybe just going through the opposing team’s lineup less than twice, before turning the game over to the bullpen. These playoffs have already seen hints of this idea this postseason with the Houston Astros. Lance McCullers, usually a starter, has had appearances from the bullpen where he has taken over a game in the middle innings (Game 4 of the ALDS, Game 7 of the ALCS) and thrown about 50 pitches, worked about three innings and gone through the opposing lineup less than two times. This idea may not even work in the regular season, but it could in the playoffs, where teams have already adapted the way they use their bullpen. The idea may not seem plausible now but in baseball, sometimes the most unimaginable ideas end up winning championships.