It's impossible to have a discussion with your friends throughout the greatest hitters and major league history without hearing the term RBI. It almost always follows the statistic of home runs. "Barry Bonds finished his career with 762 home runs and 1,996 RBIs."

But what is an RBI, and why is it a variable in determining how good a hitter somebody is/was in the context of MLB? Let's start with the definition.

What is an RBI in baseball?

RBI is an acronym that stands for run batted in. A player is credited with an RBI anytime a run scores as a result of their at-bat (with a couple of exceptions that we will get into in a minute).

If a run scores as a result of a hit, then an RBI is credited to the batter. In the case of a home run, the batter gets credit for themselves, since they crossed home plate as a result of their own hit. A player who hits a pop fly that is caught, and a player scores after tagging up (sacrifice fly), is an RBI. If the bases are loaded (man on every base) and a batter is hit by a pitch, or walked on 4 balls out of the strike zone, the runner on third is forced to score, and an RBI is credited to the batter. Lastly, an RBI can be earned if a player is tagged out or thrown out, but a run scores during the play.

When do you not get an RBI? If a run scores as a result of an error or a double play, the hitter is not credited with an RBI. So if a hitter hits a ground ball that goes through the legs of the shortstop and a run scores, the hitter does not get credit for the run (as long as the official scorer logs it as an error). If the hitter hits into a double play, and a run scores from third, they are not credited with the RBI.

Now that you know how an RBI is calculated, it's easy to understand why it is used as a variable in determining how good a hitter a player is. An RBI is a run that was scored by a team as a direct result of what a hitter did while he was in the batter's box. It represents a player you want hitting if your team has any players on base. Long story short, with 1,996 career RBIs, Barry Bonds was an amazing hitter.