Pitchers find themselves in tricky situations many times throughout a season. In these cases, we often hear commentators talk about limiting the damage, preventing as many runs as possible. This translates in manager-speak to: “Keep the goddam runners on base and off home plate.”
Left On Base Percentage (LOB%) is an estimation of the percent of runners that a pitcher was able to strand on base, as opposed to allowing them to score. While pitchers’ abilities vary to extremes, LOB% tends to fall between 65% and 75% for most pitchers. A high LOB%, like 80%, indicates that a pitcher is able to keep most of his base runners off the scoreboard. Pitchers who strike out a lot of batters and who generally keep runners off the base paths will usually see higher LOB%s, while pitchers who allow a lot of walks and strike out less batters are less likely to strand runners on base.
Even though a pitcher has some control over stranding runners, luck and team defense likely play key roles in the LOB%. Sometimes bloopers find the outfield grass with a runner on third, and other times hard-hit line drives destined for the gap get snared by middle infielders with two outs and the bases juiced. A few fortunate or unfortunate bounces in the first half of a season can raise or lower a pitcher’s ERA as much as a full run.