LOB stands for “left on base” and refers to the number of baserunners that are stranded on base at the end of an inning.
In a regulation-length Major League Baseball game, each team tries to score as many runs as possible over the course of nine innings. When a batter gets a hit or walk, he (usually) becomes a baserunner and tries to advance around the bases to eventually touch home plate. Not every baserunner will end up scoring, though, and that’s where LOB comes into play.
Let’s say a team has two runners on base with two outs in an inning, and the batter hits a pop-up that is caught by the opposing team’s fielder to end the inning. The two baserunners were left on base and did not score, so the team has two LOB for that inning. The LOB statistic is used to measure a team’s ability to drive in runners who are already on base.
It also measures a pitcher’s ability to pitch out of a jam, at least indirectly.
LOB can be a frustrating statistic for both players and fans, as it can indicate missed opportunities to score runs. Teams that consistently leave runners on base may struggle to win games, while teams that are able to capitalize on scoring opportunities will typically have more success.