Andrew Bailey and Red Sox Starting Pitching: What Shall We Do with a Tiny Sample?

Kees van Hemmen
6 min readApr 3, 2024

Red Sox starting pitching has been awesome through 6 games played in the 2024 season. Quite frankly, that might be too few games to properly do an analysis, but I’m in the business of small sample sizes — so we’re doing it anyway. Let’s take a look at what has changed for Red Sox starting pitching this season.

The following analysis is pretty simple: I compared the Red Sox starting rotation this year in terms of pitch location and usage to the same pitchers last year. This was easy, mostly because the Red Sox starters this season all started for the team last year at some point. I’ve excluded pitches thrown in relief in 2023 for consistency.

Left: 2023 Pitch Usage by Nick Pivetta, Brayan Bello, Kutter Crawford, Garrett Whitlock and Tanner Houck; Right: 2024 Pitch Usage by the same pitchers

First, let’s look at broad usage and efficacy trends. On the left we have 2023 pitch usage for Red Sox starters. On the right we have the same numbers for 2024.

There’s a lot of little stuff going on in here, but the main takeaway I have is this: the pitches that Red Sox starters have thrown most often this season are the same pitches they had the most success throwing last season. Notice that the 2023 chart is sorted by xwOBA against — basically, pitch efficacy. Meanwhile, the 2024 chart is sorted by pitch usage. The result? The order of the two charts is almost identical. I do think this is a very intentional move by Bailey: we’ve already seen Brayan Bello drop his 4-seam fastball altogether, Garrett Whitlock halve his sinker usage, and Kutter Crawford do the same with his 4-seam. Now, part of this is a clear move away from 4-seam fastballs entirely — Bailey’s 2023 Giants team threw the fewest 4-seam fastballs of any rotation in the statcast era — but I also think this is clearly a rotation counting on their best stuff, rather than trying to ‘establish the fastball.’ Notice the large uptick in sweeper and changeup use. For 4 of the Red Sox 5 current starters (Nick Pivetta, Brayan Bello, Garrett Whitlock, and Kutter Crawford) their best pitch last season by xwOBA against was either a sweeper or a changeup.

Let’s go from the process into the results for a second. Not only have Sox starters drastically changed their pitch mix, they’ve also had a massive increase in success rate in terms of converting 2-strike counts into strikeouts:

How are they doing this? Well, let’s take a look at how they were approaching 2-strike counts in 2023:

In these counts, the Red Sox current starting rotation was throwing breaking balls (sliders, sweepers, and curveballs) outside the zone a whopping 70% of the time. 46% of the time those pitches were more than 4 inches outside of the zone. This year?

15% of 2 strike pitches thrown by Sox pitchers this season have been breaking balls located inside the strike zone. That’s up from just 8.6% last season. This isn’t just due to location, it’s also due to raw usage: in 2023, Red Sox starters threw their breaking balls only 31% of the time in these counts — this year, it’s up to 44% thus far. This is the start of trend: breaking balls thrown more, and when thrown, thrown in the zone at a higher clip.

This has corresponded to an even more drastic drop in fastball usage in the same counts. Take a look: in 2023, 44% of 2 strike pitches were 4-seamers or sinkers. This year? Only 27%.

The only real change in location distribution here looks like fewer misses up, and that’s probably just due to the drop off in 4-seam usage. You don’t generally try to get swing and miss with a sinker thrown up in the zone in 2-strike counts. My main takeaway? Red Sox starters are offering hitters far less hard stuff to square up in counts where they’re already looking to protect. Makes sense to me.

Now let’s take a look at 0–0 counts. Andrew Bailey talked the other night about how, for him, the most important thing for Tanner Houck to do was to get ahead of opposition hitters. Usually this means stealing strikes with the fastball early. Has that happened?

… nope. First pitch fastball usage is down 25%. Moreover, the few first pitch fastballs that Sox pitchers have thrown this season have been located outside of the zone at a higher clip than previously. Last year, the first pitch a Red Sox starter threw in a given at bat had a 23% chance of being a fastball located in the strike zone. This year that’s down to only 16%. Meanwhile, first pitch fastballs located outside of the zone are being thrown at basically the same clip (15% of first pitches this year, compared to 14% of first pitches last year). So, rather than pounding the strike zone to get ahead of hitters, it looks like Sox starters are actually using their hard stuff as a chase pitch early in counts. The sample is too small to say whether this will last, but for now it’s something to keep an eye on.

When we look at breaking balls, the opposite trend has occurred:

First pitch breaking ball usage is up 20% across the board, and first pitch breaking balls thrown for strikes are up from 13% of first pitches to 18% of pitches. More interesting? Take a look at the location of these pitches.

Last year, Sox starters threw first pitch fastballs 30" off the ground on average. This year that’s down to 28" — probably predominantly as a result of the increased use of sinkers as opposed to 4-seamers. That, however, pails in comparison to the change in elevation for breaking balls: where last year Sox starters threw first pitch breaking balls 24" off the ground, this year that number is up to 31 (!!!) inches. That’s a 7 inch increase. Right now, Red Sox starters are throwing their breaking balls 3 inches higher than their fastballs in 0–0 counts. Talk about pitching backwards.

Now, part of this trend is due to the increase in sweeper usage — sweepers have a bit of lift, whereas sliders and curveballs typically drop. That, however, doesn’t account for a swing that large. The sample size is small, but the strategy seems clear: don’t be afraid to elevate your breaking ball. We’ll see if this continues to be an effective strategy for the Sox as the season goes on, especially as they tire and perhaps start to locate slightly worse than they have so far.

It’s worth noting that Alex Cora implied that part of the breaking ball heavy approach was due to Seattle’s lineup struggling with breaking balls, but, nevertheless, this seems like a set of trends that’s likely to continue to some extent. Jen McCaffrey of The Athletic got an awesome quote from Andrew Bailey about how he views fastballs as being the baseball equivalent of a jab in boxing — you don’t win a boxing match just throwing jabs all night. That’s already showing.

Go Sox!