In baseball and softball, an RBI is a "run batted in," and a batter receives one when a player scores after he is credited with a hit. Batters also receive one upon drawing a walk with the bases loaded.
A batter is only credited with an RBI if the runner scores after he is credited with a hit. If the batter gets on base due to a fielder error, the run is scored as "unearned." In addition, a runner who scores after a fielding error does not count as an RBI either. When a batter hits a home run, he receives an RBI for himself and for any players on base. Thus, a grand slam nets a batter four RBIs.
A batter's position in the line-up can affect his RBI total. If a batter has speedy players who frequently get on base batting before him, he is more likely to get RBIs when he hits. Because of this, baseball analysts often rely on other statistical measurements when determining how well a hitter is performing. A great lead-off hitter might now have a low RBI total because of his position in the line-up, while a mediocre hitter batting fourth is more likely to earn RBIs when he hits.