Strand rate measures the percentage of baserunners a pitcher allows that don’t end up scoring. League average is about 73%. A pitcher allows 100 baserunners and 27 of them score — his LOB% is 73%.

LOB% is one of the classic regression candidates. Pitchers running an 80%+ strand rate are usually getting lucky in high-leverage spots, and that luck doesn’t persist. Pitchers running 65%- are typically unlucky and due to improve.

The reason it tends to regress is that, over a full season, pitchers don’t have much control over which baserunners eventually score. A pitcher’s skill is captured in K%, BB%, and HR/9 — LOB% is mostly noise. When you see a low ERA paired with an extreme LOB%, expect the ERA to move toward the FIP.

What is a good LOB%?

LOB% is not directly used in NUT or FIP because it reflects situational outcomes more than pitcher skill. It still appears on Baseball Nut’s pitcher percentile rankings as a way to see whether a pitcher’s ERA is being helped or hurt by stranding runners at unsustainable rates.

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