It is often discussed in baseball that sometimes a team must “manufacture runs.” This phrase essentially means that they are trying to score more runs on fewer hits. To accomplish run manufacturing, a team will need to move runners up without getting hits. Bunting, sac flies and stealing bases are the usual approaches. We want to discuss bunting.
Of course, every team has different hitters with different capabilities and there are special situations that a general analysis cannot properly address, but our analysis will take a general approach. Using the well-established concept of run value, we will evaluate the benefit of moving a runner with a bunt. Run value is a measure of how much a specific play benefits a team compared to the play’s run expectancy. Run expectancy is a measure of the average runs scored in the remainder of an inning based on the current situation. For example, if a team has a runner on second and two outs, run expectancy would tell how many runs they can expect to score before the third out happens.
Run expectancy in each situation in the 2023 MLB season.
In the plot above you can see the run expectancy in each situation based on the data from the 2023 MLB season. Note that these averages change a little bit between seasons, but stay surprisingly consistent. Now, assume you have no outs and a runner on first. Should the runner steal second base? To answer this question analytically, we will use run value. To calculate the run value of a successful sacrifice bunt we take the ending run expectancy and subtract the beginning run expectancy. In our example we have a beginning run expectancy of 0.9 runs and an ending run expectancy of 0.71 runs. Thus, the run value of the sac bunt is 0.71-0.9=-0.19. So, the sac bunt had a negative run value on average. The same play used with one out has a run value of -0.23. We can conclude that bunting a runner to second will result in fewer runs on average. The same holds true for bunting a runner to third.
It is clear that outs are much more valuable than many people have imagined over the years. Even though it is much harder to score a runner from first than from second, sacrificing the out simply isn’t worth it on average. Of course, it is not comprehensive to think about bunting on average. Sometimes a below average hitter can be more valuable to their team by bunting in certain situations. The general approach we have taken is still incredibly useful for understanding how valuable outs are and how to maximize runs.
There is something else to consider when doing this analysis; we are not always concerned with maximizing runs scored. There are situations in which you don’t necessarily want to maximize runs, but only need to score one run. For example, the bottom of the ninth inning in a tied game. We must consider the benefit of bunting a little bit differently by asking a different question. Will a sac bunt help the team score at least one run in this situation? Now, run expectancy is not useful to us and we need to know the probability of scoring a run in each situation on average.
Run probability in each situation in the 2023 MLB season.
The plot above shows us the probability of scoring at least one run, given the current situation. Let’s revisit our previous example using what we will call run probability value. Consider the runner on first, no out scenario. We can evaluate the benefit of the bunt using the same formula we used before: ending probability minus beginning probability. We see a run probability value of 0.42-0.42=0. We can conclude that bunting a runner to second with no outs doesn’t help or hurt your chances of scoring a run on average. If we tried this play with one out we would see a run probability value of 0.21-0.27=-0.06. Again, it doesn’t help to bunt a runner to second on average.
What about bunting a runner to third? Now the analysis becomes interesting, especially considering the ghost runner rule in extra innings. If you bunt a runner to third with no outs, you get a run probability value of 0.64-0.61=0.03. The data shows that bunting the runner to third actually increases a team’s chance of scoring at least on run in the inning. Throughout the 2024 MLB season, many extra inning games were played and the bunt was rarely used. Teams should take advantage of the extra 3% chance of scoring a run in that situation.