Astros Offense: Stats Edition

The Astros’ offense has been on an upward trend. A few months ago, the Astros’ offense was ranked in the middle of the MLB pack (around 16th). Today, the Astros offense is ranked 5th, using the overall offense stat wRC+ (runs created). You may have your own ideas about the value of individual Astros’ players. You may base your player rankings on OPS, wRC+, or components like SLG.

Instead of your normal “go to” offensive stats, this article will discuss alternative advanced offensive statistics which may change your opinion about the offensive value of the individual Astros’ batters. In addition, I will also provide an update on the playoff odds of the AL West teams.

Best Astros Hitters Based on Win Probability and Run Expectancy (RE24)

Win Probability Added (WPA) and Run Expectance 24 (RE24) are probabilistic stats which measure offensive performance, but include context of player’s performance. An example of context: a grand slam HR is worth three runs more than a solo HR, and WPA and RE24 recognize that fact. Similarly, a walk with the bases loaded has the same value as a solo HR, which is one of the reasons RE24 is a good measure of all types of skills, not just hitting HRs.

WPA measures the player’s contribution to increasing or decreasing the probability of winning the game, based on the win probability before and after the pate appearance. Two main differences distinguish RE24 from WPA. RE24 measures the change in probability of scoring runs at the more granular inning level, insteaad of game level. In addition, RE24 excludes leverage associated with game score as a consideration, whereas WPA is highly influenced by the game score. WPA is considered a more descriptive statistic, telling us what happened in the game, but is not predictive. RE 24 is more dependent on the player’s hitting skills, and how those skills are used in various base/out situations. WPA is appropriate for MVP discussions, but RE24 is more reflective of the contribution provided by the player’s skills

RE24 provides one of the best measures of an offensive player’s production. In my view, RE24 is a measure of production which is superior to the traditional RBI (runs batted in) statistic. That’s because RE24 encompasses more of the skills that the player employed to increase the probability of scoring run(s), such as advancing runners and avoiding double plays. Keep in mind that RE24 is expressed as runs above average, meaning that it reflects the change in run expectancy which is higher/lower than the average MLB player in that situation. The table below (from Fangraphs) shows the current WPA for Astros’ hitters with a positive RE24. Runs above average for RE24 can be converted to Wins Above Average by dividing by 9.65.

One of the differences, compared to the standard linear weights stat, is that Altuve is 2d in wOBA, but falls to 5th in RE24, while Alex Bregman is 5th in wOBA but is higher at 3d in RE24. This is partly because RE24 is a counting stat, and injury-plagued Altuve has less plate appearances than Bregman. Taking into account that Alvarez was injured for a substantial part of the year, it is even more amazing that he leads the team in RE24.

The Major League rankings for WPA: Tucker (4th), McCormick (8th), Alvarez (11th), and Bregman (29th). The Major League RE24 rankings: Alvarez (8th), Tucker (10th), Bregman (13th), and McCormick (19th). Both McCormick and Alvarez would rank even higher on the MLB RE24 if they had not suffered injuries that reduced their plate appearances.

To illustrate the difference between wOBA and RE24, the Astros team rank is 5th in RE24 but is lower, at 7th, in wOBA. This seems to indicate that the Astros’ hitters are better when the situational context is included.

Interpreting the Astros x- stats

Another family of advanced stats are the Statcast “x-” stats (i.e., x-BA, xwOBA, x-SLG). The x-stats compile the offensive measure based on physical characteristics (such as exit velocity and launch angle) of the hitting event and the “expected” outcome. The difference between xwOBA and actual wOBA may indicate whether the hitter has been lucky or unlucky. For instance, a batter may have hit a lot of very hard hit line drives right into the glove of the fielder.

Sometimes players’ xwOBA is represented by fans as superior to wOBA because the former is viewed as more predictive of what will happen in the future. But this isn’t necessarily true. Fangraphs’ Dan Symborski wrote an enlightening article on how best to use the x-stats. As noted in the article, there is some debate as to whether x-stats have any value at all as a predictive offensive measure. His conclusion: the x-stats by themselves are not better than the actual stat, but the x-stats are useful in combination with the actual stats.

Some points he makes: (1) x-stats when used alone are not significantly more predictive than the actual stats in projecting the next year. (2) Sometimes stats become more predictive when used in combination. As an analogy, OBP and SLG, when used alone have limited predictive value for runs scored, but when used together OPS has high predictive value for runs scored (>90%). (3) A stat which combines actual wOBA and xwOBA has higher predictive value than either measure alone. (4) In combining the two stats, the number of plate appearances is important for determining the weights applied to each.

Symborski provides this formula for weighting the actual wOBA with xwOBA: PA / (766 + PA). So, I used that formula to calculate a Combined wOBA Stat for the leading Astros’ hitters.

Combined wOBA stat (actual wOBA weighted by xwOBA)

Alvarez 0.417

Tucker 0.388

Y. Diaz 0.360

McCormick 0.358

Altuve 0.355

Bregman 0.349

Kessinger 0.318

Pena 0.309

Dubon 0.298

Abreu 0.294

Meyers 0.292

Julks 0.291

All of the above hitters have a xwOBA higher than their actual wOBA, except for McCormick, Bregman, Altuve, Pena, Meyers and Dubon, who have an actual wOBA higher than their xwOBA.

Update on AL West Playoff Odds

As I have done in past articles, I will look at the Astros’ current probabilities for the playoffs. For the reasons stated in previous articles, I will rely on the Fangraphs daily playoff odds.

Compared to last week, the Fangraphs’ model likes the Astros’ current position. The Rangers’ odds continue to tumble, with the Mariners holding the advantage over them. The Astros’ odds of winning the AL West are above 50%, and the probability of making the playoffs is 95%. The Astros also hold a 13.5% probability of winning the World Series, which is the highest among AL teams.

Win Division Odds / Playoff Odds

Astros 53.5% / 95%

Mariners 32.0% / 86.5%

Rangers 14.5% / 70.6%