A look at 2d half run expectancy

We often measure players’ performance using non-contextual stats. But certain contextual stats may provide insight on the relative value of individual players’ performance. This article will examine Astros’ individual 2d half performance using run expectancy stats, which are context dependent.

Run expectancy stats are contextual, taking into account the sequencing and timing of hits and outs. The more commonly used batting stats are based on the league average linear run impacts of hits and outs over a season. Examples include wOBA, wRC+, and wRAA. These are linear weight statistics which place a value on singles, doubles, triples, and home runs based on the average throughout the season. And the player’s average wOBA or wRAA is rolled into the player’s fWAR or bWAR valuation. However, if we choose to utilize a contextual stat, like Run Expectancy (RE 24), the player’s value as measured by WAR, might be considerably higher or lower.

RE24, measures the value of a hit or out in each of the 24 base-out states recognizing that 24 combinations of base-out situation exist). RE24 does not measure timing of leverage (i.e., inning and score), but relies on the base-out situation. Because RE24 is situational and considers factors like productive outs and base running, conceptually it is more informative of skill and repeatability than WPA. There are many base-out situations in which the batter may adjust his approach at the plate. At the team level, RE24 may tell us which teams are better at converting hits and outs into runs. But, more to the point, the RE24 tells us about the hitter’s consistency at improving the run expectancy in each at bat.

Let’s look at the best Astros’ hitters based on RE24 during the second half of this season.

Run Expectancy Above Average

Alvarez 7.42

Pena 4.42

Walker 2.91

Diaz 2.42

Correa 1.69

Caratini 1.26

Alvarez only played 17 games in the second half, but he is the leader in Astros’ RE24 during this period—which tells you something about his productivity when he returned from the IL. He was a big cog in the Astros lineup before he went down with an ankle sprain earlier this week.

It’s also interesting to compare hitters’ RE24 with the non-contextual runs above average (wRAA). Pena, Walker, Diaz, and Caratini have a 2d half RE24 higher than their second halff wRAA. This indicates that they have improved run expectancy more than you would expect from the linear weights measure of offense. This is particularly true of Yainer Diaz who has a slim negative wRAA on a non-contextual basis, but put up the fourth best positive run expectancy. While Diaz has poor “average offensive stats” in the second half, he has been pretty good at improving run expectancy. Correa, on the other hand, is the opposite. He is 5.22 wRAA compared to 1.69 RE24.

Hitting into double plays can really cause a hitters’ run expectancy stats to take a hit. Correa and Diaz are 2d in Astros’ GIDP (six) in the second half. This may have diminished Correa’s RE24, but for whatever reason had less impact on Diaz’s RE24. Perhaps Correa’s GIDPs tended to occur with no outs, while Diaz’s situation tended to be 1 out.

In the second half, Altuve (-8.31), Cam Smith (-12.20), and Dubon (-7.20) have done the most damage to Astros’ run expectancy in the second half. Each of these hitters has negative wRAA in the second half, but their contextual wRE24 is even worse than the non-contextual offensive stat. Altuve and Smith show particularly large margins between the situational stat, RE24, and wRAA. Altuve leads the Astros in GIDP during the second half (10) which may contribute to this margin between linear average stat and run expectancy. Cam Smith may have been a bigger drag on the second half lineup than I expected.

The RE24 stat can also be used to compare the starting pitchers’ performance in the second half. This tells us how much the starting pitcher improved run expectancy as risky situations arise during his pitching stint. The positive RE 24 in the second half for Astros pitchers:

Improve Run Expectancy (2d Half)

Brown 11.15

Alexander 6.61

Walter 4.15

It’s not surprising that Hunter Brown leads the list. But Jason Alexander has been surprisingly good at managing base/out situations. And Walter’s run expectancy highlights how much his loss to injury hurt the Astros in the second half.

Colton Gordon and Framber Valdez have been particularly bad at handling base-out situations in the second half. The RE24 for those two left handers: Gordon (-7.29) Valdez (-9.87).

The significant negative run expectancy exhibited by Valdez may reflect the tendency to implode when difficult situations or bad luck arise. This is a concern for possible future post season starts. For each of his post season series in 2023 and 2024, Valdez provided a significant cWPA (championship win probability added): -2.6%, -8.1%, and -1.1%. This contrasts with his cWPA in the 2022 ALDS and ALCS: +3.8% and +12.8%.

I have seen some speculation on social media that the advent of the pitch clock may have contributed to Valdez’s implosions. The theory is that Valdez previously dealt with those stressful situations by taking his time in order to change his mindset.

Saber expert Tangotiger pointed out some support for the hypothesis: Framber formerly took more time in 2022 (and before) with runners on base. But very little has changed, in terms of tempo, with bases empty.

This explanation has some relevance to base-out situations and might provide additional context for Valdez’s poor RE24 in the second half of the season. In any event, the Astros depend on Framber Valdez and need some improvement in stressful base-out situation over the remaining few games and into the playoffs.

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