Lower walk rate is the reason why Rays and Giants’ relief pitchers are so good.

*This story was published on September 26th 2021 in Japanese.

Rays Win Historic District Championship

With a win over the Marlins on September 25, the Rays won the district championship for the second year. The Rays are known for introducing creative strategies such as bullpen days and openers earlier than other teams, but this year, not a single pitcher has reached the required number of innings pitched. Currently, R. Yarbrough has the most innings pitched on the team at 150.1, but considering the number of games remaining, it is unlikely that he will reach the minimum number of innings pitched.

Last year, the Rays did not have a pitcher who reached the qualified innings. However, since the last season consisted of 60 games, it was an unusual situation, so it was not that difficult for the Rays to overcome the hurdle with the help of the bullpen. Also, although there were no pitchers who had reached the minimum number of innings pitched, the team had talented starting pitchers such asBlake Snell and Charlie Morton.

However, this season, Snell and Morton left the team, and Tyler Glasnow, who pitched well in the early innings, also left the team because of an injury. Nevertheless, the Rays’ pitching staff still leads the league in both team batting average and team FIP. So what is the biggest reason for this good performance? Yes, a strong bullpen.

The Rays bullpen has a variety of talent, from veterans such as D. Robertson and C. McHugh, who both competed in the Tokyo Olympics, to up-and-coming youngsters such as L. Patiño, who was acquired in the Snell trade last offseason.

Like the Rays, the Giants have a unique group of members in their bullpen. The Giants lost starting pitchers J. Cueto and A. Wood at the end of August. So they turned two of the five days into bullpen days to fill these two holes. This secret plan has worked, no doubt, due to the leaders’ confidence in the relievers.

So far, I have praised the bullpens of the Rays and Giants, who have been on a roll this season. So I wonder if there are any similarities between the bullpens of these two teams. And that commonality is the central theme of this article.

Commonalities between the Rays and Giants bullpens

The commonality is that the two teams’ bullpens have “not so high strikeout rates, but low walk rates.

Many people think of Craig Kimbrel, Aroldis Chapman, and Kenley Jansen as the leading relief pitchers of the 2010s. This is because they all had excellent strikeout ability. And that ability to strike out has been recognized as an essential element of a strong bullpen. The idea behind this is that strikeouts are not dependent on luck (such as a fielder’s defense).

In fact, the top four teams in FIP in 2018 all had K/9s over 10.00, and in a sense, it was even a showdown of how many strikeouts a team could get. Similarly, in 2019, the top FIP teams all had K/9 over 9.00, with the only exception being the Giants at 8.87.

However, looking at the K/9 of the top FIP teams this year, 2021, Marlins, in second place, has a K/9 of 8.39 (27th), and Mariners, in third place, have a K/9 of 8.89 (22nd), which is not high. Conversely, Reds (10.48) and Cubs (10.20), with high K/9, also show sluggish FIPs of 4.56and 4.48, respectively.

As for the strength of the correlation between K/9 and FIP, the correlation coefficient has changed between 2018 and 2019, and 2021. The correlation coefficient between the two is -0.80 in 2018, -0.63 in 2019, and -0.19 in 2021, indicating that the correlation is weaker in 2021 (higher K/9 is better while lower FIP is better, so the correlation coefficient between the two is negative).

Thus, the K/9 of teams with superior FIP is not so high this year. So what makes the team with an excellent FIP superior? It is BB/9. Rays, Giants, Marlins, and Mariners have excellent FIPs. They are in the top 5 of the 30 teams in BB/9 this season.

I should also mention that the correlation coefficient between BB/9 and FIP is 0.44 in 2018, 0.65 in 2019, and 0.59 in 2021. In other words, I think it can be interpreted that there is some degree of correlation without much change over the three years.

Hypothesis on why the Rays and Giants lower BB/9 instead of raising K/9

So why do SF and TB have lower BB/9 instead of higher K/9? I have two hypotheses about this, which I would like to share.

Hypothesis 1: The prevalence of defensive shifting has improved defensive accuracy → No need to fear in-play anymore?

As I mentioned at the beginning of this article, strikeouts have been emphasized because of the idea that “strikeouts are not affected by luck (such as the defensive ability of the fielder). However, in extreme cases, there is no need to worry about strikeouts as long as the fielder makes a complete out, even if it is a ground ball or a fly ball. Strikeouts are essential because there is a difference in the probability of getting an out between a strikeout and a ground ball or fly ball, and there is no difference between a strikeout and a ground ball or pass ball if a ground ball or fly ball can be made into an out without fail.

Indeed, this is a powerful story and one that is unrealistic. However, there have been several defensive shifts in MLB in recent years, and the impact has been tremendous.

The league-wide DRS has turned significantly positive since 2016 and is almost sure to set a record in 2021 at +436. Thus, considering that MLB’s overall defensive performance has improved and the probability of getting an out in play has also increased, we may not have to focus so intensely on strikeouts.

Let us compare a player who has a high strikeout ability but often gives up four hits by pitches and a player who has a moderate strikeout ability but rarely gives up four hits by pitches. In this case, the former would have been valued more highly in the past. However, suppose the latter player’s probability of giving up a run due to a hit by pitch decreases due to improvements in defense, and the likelihood of giving up a run due to a hit by pitch falls below the likelihood of giving up a run due to a hit by pitch. In that case, the two players will be evaluated oppositely. This is Hypothesis 1.

Hypothesis 2: Relief pitchers will become starters.

With the spread of strategies such as openers and bullpen days, it has become commonplace for relief pitchers to pitch in the first inning or early innings of a game. So naturally, you do not want to give up the first run, and every team wants to avoid giving up too many runs in the early innings of a game.

In such a situation, the starter or reliever who pitches early in the game is required not to break up the game. In other words, relief pitchers are now expected to have the same abilities required initially of starters. The Rays and Giants are looking for relievers who have low BB/9 and do not break up games. This is hypothesis 2.

Conclusion

In this issue

(1) The correlation between K/9 and FIP is weakening.

2) That teams with superior BB/9 are leaving good FIP

(3) The hypothesis behind this

(3) The hypothesis behind this trend. Of course, we don’t know if this trend will continue, but we will first look to see what the Rays and Giants relievers with excellent BB/9 will do in the playoffs.

Photo by Charlie Lyons-Pardue