Stopping on Nine: Evidence of Heuristic Managerial Decision‐Making in Major League Baseball Pitcher Substitutions

Economic agents who exhibit left digit bias over‐emphasize round numbers. Using data on managers' pitcher substitution decisions in Major League Baseball, I find that managers remove starting pitchers more often when the next pitch will result in a pitch count ending in zero. Unlike counts ending in nine, pitch counts ending in eight do not exhibit higher substitution rates despite the fact that pitchers usually throw multiple pitches before the manager's next decision opportunity. Managers apparently use rules‐of‐thumb that emphasize leftmost digits and ignore at least some future consequences of present actions. However, these significant biases disappear when the stakes are high. I find no evidence of disproportionate substitutions on the nine's in close games, and the final digit of the pitch count does not discontinuously affect the probability of winning. Managers act in a manner consistent with rational inattention, using heuristics only when the stakes are low.