Revisiting Guillen Number: Percentage of Runs Scored Via Home Run

    Baseball Prospectus used to track a metric called Guillen Number, which was defined as “the percentage of a team’s runs which come via home runs.” It’s always been an interesting number to me, especially as a fan of the Yankees, a team that consistently is near the top in that percentage, and as a fan who has observed the shift in the game becoming more home run focused in general. I like this metric because it describes exactly what it describes: how often are teams scoring from home runs. It doesn’t describe how many runs that team scores or how good that offense is, but it gives implications that fans care about. Are teams with high Guillen scores reliant on home runs to score? Is it a bad thing to have a high Guillen number?

    My main motivation for revisiting this metric is because it’s hard to find. I don’t believe Baseball Prospectus tracks it anymore, and easy access websites like Baseball Reference and Fangraphs would require a lot of clicks and using your calculator to figure out what your favorite team’s Guillen number is. Thanks to downloading play-by-play data from Retrosheet, now I can calculate that myself. For this article, I'm looking at 1960 onward only.

    The second motivation is to analyze some of those questions I mentioned at the beginning. We’ve always known hitting home runs is a good thing—obviously—and the best offenses hit lots of home runs. There has always been a stigma though against teams that hit lots of home runs. As fans, we want offenses that can “manufacture runs” in diverse ways outside of the home run. And in recent years, it’s been written that with pitching quality higher than ever, especially in the playoffs, hitting home runs for offense might be more reliable than the traditional way.

How has the way offenses score changed over time?

    Let’s divide the way teams can score into four categories: home runs, hits (other than home runs of course), other balls in play (sac flies, errors, fielders choices, etc.), and then any other way to score (wild pitches, bases-loaded walks and HBPs, etc.).

    Looking at the chart above, the feeling that offenses have gotten more homer-reliant is obviously back up by the numbers. Starting in 1992, when home runs accounted for 28.1% of runs scored, the percentage steadily increased until baseball settled into the Steroid Era, with the Guillen Number hovering around 36% from 1999 to 2006. In 2014, it dipped down to 33.4%. What came next was the Juiced-Ball Era, and the previous highs seen during the Steroid Era became laughable. In 2016, the league wide Guillen Number was over 40% for the first time. In 2019, we saw the percentage of runs via home run exceed the percentage of runs via other hits for the first time, something that continued through 2021. 2019 was also the highest Guillen Number ever at 45.2%.

    How does this compare to the postseason? The postseason of course comes with much smaller sample sizes of games, but I was curious if it reflected similar trends, if not more extreme. In recent years, postseason battles often feel like a solo home run contest, with runs becoming a real scarcity as teams deploy the best pitching they possibly can for 9 innings each game.

With the smaller sample, especially up until 1968 when the most postseason games possible was 7, it’s no surprise there were wonky seasons with high Guillen Numbers. In recent years though (and with larger sample sizes since the 12-team playoff implemented in 2022), the increase in Guillen Number in the playoffs is noticeable. Let’s isolate the graph to just comparing Guillen Number, not other run type percentages, between the regular season and postseason in the 12-team-playoff era.

Overall, this is a regular season Guillen Number of 40.7% across 86,206 runs scored compared to 47.0% across 1,368 playoff runs scored. A 2-sample test for equality of proportions shows this as statistically significant, with a 95% confidence interval between a 3.6 and 9.0 percent increase in the postseason.

How do teams with high Guillen Numbers perform offensively?

So, is having a high Guillen Number a bad thing? If your team is too reliant on scoring via home runs, does that make your offense worse? Ultimately, I’m not really sure how we can think about that aside from seeing how it correlates with runs scored.

In the year 2025, there was a positive correlation between Guillen Number and Runs/Game, with a correlation coefficient of 0.401. What about if we look at a larger sample in the expanded playoff era? Since we’re looking at multiple years, I’ll use a standardized runs/game—essentially how many runs/game compared to league average.

The correlation coefficient is 0.365. If we look at all seasons, 1960 to present, and its correlation with standardized runs/game, the correlation is 0.246. There seems to have always been some positive correlation, but more so in the current game now.

How does Guillen Number correlate with playoff offense? In the expanded playoff era, the correlation coefficient is 0.238, but with a smaller sample of 48, it fails a Pearson correlation test that the true correlation is not equal to zero.

 

Guillen Number Leaders

What are the highest Guillen numbers ever?                     

    No surprise that the highest scores are all recently, especially in the Juiced-Ball Era and with the 2023 Braves, who tied the 2019 Twins for most home runs in a season, high up. The standout here is the 2010 Blue Jays, who had a Guillen score of 53.1% despite a Guillen Number league-wide of 34.4%.  

When we look at highest standardized Guillen Numbers of all time, it’s no surprise to see those 2010 Blue Jays at the top:

   

                                                     

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