Today I want to teach you all about two of the more simple, yet more telling statistics to reference when evaluating a pitcher. You can refer to these for any type of pitcher (starter, reliever, closer).
K%, or strikeout rate, and BB%, or walk rate, are exactly what they sound like: the rate at which pitchers strikeout or walk hitters. Note: these rates are on a per plate appearance basis. This allows K% and BB% to deviate from K/9 and BB/9, which tell us how many strikeouts or walks a pitcher has on a per inning basis.
Therefore, we can visualize these metrics as follows:
K% = K / PA
BB% = BB / PA
Real Examples for Starting Pitchers (2025)
Using the 2025 MLB regular season as an example, the 10 best K%s among qualified starters were (per FanGraphs):
- Tarik Skubal, 32.2%
- Garrett Crochet, 31.3%
- Dylan Cease, 29.8%
- Paul Skenes, 29.5%
- Yoshinobu Yamamoto, 29.4%
- Jesús Luzardo, 28.5%
- Joe Ryan, 28.4%
- Hunter Brown, 28.3%
- Freddy Peralta, 28.2%
- Jacob deGrom, 27.7%
Skubal and Crochet are the two AL starters gunning for the AL Cy Young Award for 2025, while Paul Skenes is all but guaranteed the NL Cy Young. K% seems to be a telling metric in that regard.
Now let’s look at the lowest BB%s among qualified starters for 2025 (per FanGraphs):
- Zack Littell, 4.2%
- Tarik Skubal, 4.4%
- Brandon Pfaadt, 4.8%
- Bryan Woo, 4.9%
- Sonny Gray, 5.0%
- Kyle Freeland, 5.4%
- Logan Webb, 5.4%
- Christopher Sánchez, 5.5%
- Joe Ryan, 5.5%
- Jacob deGrom, 5.5%
(It’s worth noting that Crochet and Skenes were the next two pitchers on the list at 5.7% BB%. )
There are some new names on this list. Littell, Pfaadt, Woo, Gray, Freeland, Webb, and Sánchez all had tremendous ability to limit walks. We still see some elite names in there: Skubal, Ryan, deGrom.
Now, if you ask casual baseball fans, no one’s going around and saying Zack Littell or Brandon Pfaadt, or Kyle Freeland are elite pitchers, and all due respect to those guys. Zack Littell held a 17.1% K%, Pfaadt a 19.2% K%, and Freeland a 17.5% K%. They clearly threw strikes, but they didn’t overpower hitters with strikeout stuff.
The best pitchers are able to combine the two: high K% coupled with low BB%. Think Skubal, Crochet, Skenes. Joe Ryan isn’t talked about enough. Jacob deGrom is still elite after surviving his first whole season in years!
In the back end of starting rotations is where you’ll find strike-throwers like Littell or Pfaadt. Guys who can avoid walks and strike a guy out here and there. These are innings-eaters who can be very valuable to a winning team’s success.
Real Examples for Relief Pitchers (2025)
Relievers’ strikeout and walk rates can be contextualized slightly differently. Because relief pitchers are expected to hold back nothing, they aren’t going to have the same command that a starting pitcher would, but they are likely going to get hitters to miss more often than not. Therefore, some relievers will have very high K%s and relatively high BB%s compared with starters. Again, the best of the best will have high K%s and low BB%s, but higher BB%s aren’t as concerning with relief pitchers if they can get the strikeouts.
The 10 best K% for qualified relievers in 2025 were (per FanGraphs):
- Mason Miller, 44.4%
- Edwin Díaz, 38.0%
- Aroldis Chapman, 37.3%
- Josh Hader, 36.9%
- Jeremiah Estrada, 35.5%
- Bryan Abreu, 35.5%
- Griffin Jax, 35.4%
- Devin Williams, 34.7%
- Cade Smith, 34.7%
- David Bednar, 34.3%
See what I mean?
Mason Miller is unbelievable, striking out close to half the batters he faces. He throws perhaps the hardest fastball in baseball, and pairs it with a devastating slider with command, so this makes sense. Díaz, Chapman and Hader are perenially some of the game’s best relief pitchers year in, year out.
Now let’s take a look at the 10 lowest BB% among qualified relievers in 2025 (per FanGraphs):
- Tyler Rogers, 2.3%
- Steven Matz, 4.0%
- Bryan King, 4.0%
- Taylor Clarke, 4.4%
- Gabe Speier, 4.5%
- Tanner Banks, 4.6%
- Justin Wrobleski, 4.8%
- Jose A. Ferrer, 4.9%
- Valente Bellozo, 5.0%
- Dylan Lee/Andrew Kittredge, 5.3%
Not many household names here. That’s likely because there aren’t the flamethrowing relievers we see on X throwing triple-digits and hyping up the crowd. Gabe Speier’s 33.7% K% is the best on the list by a wide margin, but everyone else shines with their ability to limit walks.
To give you an idea of what the top relievers in the game put up in terms of BB%, let’s go back to that top-10 K% list among relievers and list their walk rates:
- Mason Miller, 12.0%
- Edwin Díaz, 8.1%
- Aroldis Chapman, 6.6%
- Josh Hader, 7.8%
- Jeremiah Estrada, 8.9%
- Bryan Abreu, 10.5%
- Griffin Jax, 7.3%
- Devin Williams, 9.7%
- Cade Smith, 6.3%
- David Bednar, 7.6%
So despite striking out, by far, the most hitters on a per plate appearance basis, Miller walks 12.0% of hitters he faces. He strikes so many out that it’s no cause for concern.
It’s to be expected that these guys walk a few more hitters than others, as they have such great velocity and sometimes it can be hard to tame. When they walk so many guys that it affects the amount of runs they allow, then it becomes problematic.
K-BB%
To get a more all-around understanding of how often a pitcher gets strikeouts and limits walks, we can use K-BB%, which is just K% – BB%.
Mason Miller is a perfect example to use when explaining this metric. I mentioned how he strikes hitters out at an unprecedented rate, but walks more hitters than other top relievers. Because he strikes so many out, he can live with the walks. His 32.5% K-BB% is still number one in the MLB among relievers.
Here’s the list for highest K-BB%s among qualified relievers in 2025 (per FanGraphs):
- Mason Miller, 32.5%
- Aroldis Chapman, 30.7%
- Edwin Díaz, 29.8%
- Gabe Speier, 29.2%
- Josh Hader 29.1%
- Cade Smith, 28.3%
- Randy Rodríguez, 28.3%
- Griffin Jax, 28.1%
- David Bednar, 26.7%
- Jeremiah Estrada, 26.6%
Pitchers with high K% and low BB% will dominate this list of top K-BB%s. Without knowing the specific K% and BB% of a pitcher, you can find out in just one number how good they have been this season pretty reliably.
Here is the same K-BB% list for qualified starting pitchers in 2025 (per FanGraphs):
- Tarik Skubal, 27.8%
- Garrett Crochet, 25.7%
- Paul Skenes, 23.7%
- Joe Ryan, 22.8%
- Bryan Woo, 22.2%
- Jacob deGrom, 22.1%
- Sonny Gray, 21.6%
- Jesús Luzardo, 21.0%
- Christopher Sánchez/Logan Webb/Yoshinobu Yamamoto, 20.8%
- Hunter Brown, 20.4%
The top 3 starting pitchers on this list are in their respective Cy Young races, while the rest are very-much-elite pitchers in the MLB. K-BB% encompasses a pitcher’s ability to strike hitters out and limit walks very effectively and succinctly.
For further reinforcement, here are the last 5 years of Cy Young award winners and their K-BB%s (per FanGraphs):
2024 – AL – Tarik Skubal – 25.6%
2024 – NL – Chris Sale – 26.5%
2023 – AL – Gerrit Cole – 21.2%
2023 – NL – Blake Snell – 18.2%
2022 – AL – Justin Verlander – 23.4%
2022 – NL – Sandy Alcantara – 17.7%
2021 – AL – Robbie Ray – 25.4%
2021 – NL – Corbin Burnes – 30.4%
2020 – AL – Shane Bieber – 34.0%
2020 – NL – Trevor Bauer – 29.9%
K% and BB% versus K/9 and BB/9
I briefly mentioned at the top two similar metrics: K/9 and BB/9. These numbers are also strikeout and walk rates, however they are on a per inning basis. To calculate K/9 and BB/9, you must take a pitcher’s total strikeouts (or walks), divide by the total innings he pitched, before finally multiplying by 9, as there are 9 innings in a regular baseball game.
How do these differ in practice? Well, let’s say a pitcher faces 3 batters and he strikes out one of them. That pitcher has a 33% K% because in 3 plate appearances, he struck out 1 batter.
Now, let’s say another pitcher strikes one batter out, then he allows a hit and a walk before finally retiring the last two batters on fly outs. That pitcher’s K% is 20% because he struck 1 of 5 batters he faced out. However, both pitchers will have the same K/9.
Because both pitchers only pitched 1 inning and struck 1 hitter out, they will be evaluated similarly when we look at their K/9. Their K/9s will both be 9. However, we saw earlier how their K% were more representative of how efficiently they struck batters out in the context of their total batters faced.
That’s why I tend to only consider K% and BB%.
Conclusion
I hope this made sense, and you see how such simple metrics can tell you a whole lot about the pitcher you are evaluating.
In the coming days, I would like to take a look at K%, BB% and K-BB% correlate to overall run-limiting numbers such as ERA or FIP, so that we may get further evidence of their importance. Until then, take a look at some of your favorite (or least favorite) pitchers and see how their numbers stack up against the MLB’s elite.
Inner Half 