Leverage Over Rest: The Hidden Logic Behind Bullpen Usage

Coming out of the All-Star break, every team faces the same reality: the second half is a war of attrition, and the bullpen is often the first unit to crack. With workloads piling up and health concerns rising, how relievers are deployed takes on outsized importance. Are teams setting themselves up for a strong finish, or slowly wearing down the arms they’ll need most in September? Today, we take a hard look at how often relievers pitch based on days of rest and game entry point, revealing the trends that could decide who holds up and who runs out of gas.

Does Rest Matter for High-Leverage Relievers?

Unequivocally, yes managing a reliever’s workload is a season-long balancing act. Teams constantly juggle rest and availability, especially in high-leverage situations. To break it down, we’re focusing on each team’s top three relievers, identified by their cumulative impact on win probability—consistent with the approach we’ve used in past analyses. All data is from the completed 2024 season, giving us a full-picture view of usage trends and patterns.

From there, we’ll examine how these top relievers are used across three key game states: when their team is down, tied, or up.

Our first step? Identifying league-wide trends in how relievers are deployed in these situations—and what that reveals about usage patterns over the course of the season.

Going in, the assumption is simple: teams are more aggressive with reliever deployment when arms are fresh, and more cautious when fatigue sets in. But do the numbers actually support that?

This won’t give us the full picture—reliever health, velocity trends, and individual recovery rates all play a role—but it’s a critical starting point. Let’s dive into the initial results.