Overview
Run expectancy quantifies the average runs expected to score from a specific base-out state through the end of an inning, calculated from historical data. For example, runners on first with no outs yields approximately 0.85 expected runs; runner on second with no outs yields approximately 1.10. This metric is essential for evaluating tactical decisions like stolen bases and sacrifice bunts. The stolen base break-even point of roughly 70% success rate derives from run expectancy changes. Sacrifice bunts reduce run expectancy in most situations, challenging their perceived effectiveness as run-scoring tactics.