A Playoff Pitching Primer

The playoffs feature the best teams, with the best hitters squaring off against the pitchers with the best stuff. The stakes and the quality of the competition force teams to respond to fluctuations in leverage more quickly than they would in the regular season. This response makes sense: every change in win probability has an outsized effect on championship probability, so major league clubs act accordingly.

In his dissection of Kevin Cash’s decision to pull Blake Snell in the sixth inning of Game Six of the 2020 World Series, Ben Lindbergh pointed out that starting pitchers leave playoff games earlier than regular season contests, with relief pitchers now throwing the majority of playoff innings. Lindbergh also noted that more playoff starters threw 3 1/3 innings or fewer in 2020 than went at least six, a product of teams’ acceptance of the third time through the order penalty. The third time through the order penalty is real, especially for starters who lack deep repertoires. Removing starters after they turn the lineup over once or twice in favor of a high-octane bullpen arm throwing 97 mph with a slider gives the pitching team a better chance of recording an out in situations where the outcome of the game hangs in the balance.

With starters aware that they are on a short leash and likely won’t see a hitter more than once or twice, I figured it was worth looking at how pitch usage changes in the postseason. I pulled every pitcher who threw at least 50 pitches in both the regular season and the playoffs from 2015-20. I calculated each pitcher’s pitch usage in the regular season and playoffs separately and took the differences in pitch usage for each pitch. My hypothesis was that hurlers who feature a bevy of different pitches would lean more on their more trusted offerings knowing they likely won’t be asked to go deep into the game and will be pulled at the first sign of any trouble. Similarly, I thought that pitchers who employ a limited arsenal would trust their favorite pitch with the increased pressure of getting their clubs back to the dugout without allowing runs.

Surprisingly, pitchers didn’t make a significant alteration to their mix; on average, they used their most-used pitch in the regular season about one percentage point more in the playoffs. But when you break it down by pitch type, a more interesting trend reveals itself:

Pitchers who rely on fastballs (sinkers and four-seamers) as their primary offering do not see much of a change. This drags the average down because more often than not, a fastball variant is a pitcher’s top pitch. But for pitchers who rely most on pitches we traditionally call secondaries (breaking and offspeed pitches), there is a substantial shift. Pitchers who use their knuckle curves and curveballs the most see a rise in usage of 11.4 and 7.5 percentage points, respectively, while those who prefer a changeup increase their usage by 14.5 percentage points:

We can see that regardless of where a pitch places in a pitcher’s repertoire, there is a substantial ramp-up of secondary pitch usage come October. When you look at the distribution of those changes, however, a finding reveals itself that lines up with Ben Clemens’ and Eno Sarris’ prior work on the increase in breaking ball usage at the expense of fastballs in the regular and postseason, respectively:

Overall, here are the results for pitchers’ usage shift based on the hierarchy of pitches in their arsenal:

A careful reader might quibble with the information I am displaying here: how can each pitch, ranked one through four, be used more on average in the playoffs? That’s a good question, wise reader. This does not pass the proverbial sniff test. But I have an explanation! Every pitcher has a primary pitch. Every pitcher has a pitch he turns to second-most often. But not every pitcher has a third or fourth offering in their repertoire. Thus, the changes in usage by pitch rank do not totally reflect the distribution of arsenal depth among these pitchers, of whom there are just under 600. This effect can be visualized with a chart similar to the one I showed above. Instead of using pitch type, I used change in pitch usage by pitch rank:

The distribution for top pitches is much flatter than the rest of the distributions because pitchers are going to change their game plan in the playoffs depending on how many pitches they throw. To further demonstrate the oddity in the data presented above, I separated pitchers based on how many types of pitches they actually throw and then calculated the same deviations between regular season and playoff usage:

For additional context, the length of the bars represents a standard deviation among players in that pitcher population. Two-pitch pitchers tend to lean on their second pitch more in the playoffs than in the regular season all else being equal, but almost as many throw their primary offering more in the playoffs as those who do so less. Pitchers who have a three-pitch mix go to their top pitch comparatively less than their two-pitch peers, adding usage to both their second and third most-used pitches in the postseason. Pitchers who throw at least four pitches use their primary pitch less on average and really start to dig into their bag of tricks, utilizing their more tertiary offerings much more often in the playoffs, with their secondary pitch usage basically staying the same between the regular season and playoffs. These pitchers are generally starters.

What did we learn? Pitchers with more limited arsenals do not show a discernible shift in their plan of attack across the population. Often, these pitchers throw their secondary offering more in the playoffs, but many decide to go more to what they trust most, increasing their usage of their top pitch. For the pitchers with the deepest of repertoires, there is a more obvious change in behavior. While some of the pitchers in this cohort are relievers, the majority are starters. Thus we can draw as a reasonable conclusion that starting pitchers change their behavior more in the playoffs (at least compared to the pitchers with a more limited set of offerings). They choose to dig deeper into their toolbox, presumably believing they need to create uncertainty about what pitch is coming next to get the best hitters out in October. As we move into the playoffs, I think it is worth paying close attention to starting pitchers and how they choose to carefully attack hitters in the games with the highest stakes. More often than not, they will use everything they have to get those precious outs as their clubs look to capture the World Series trophy.