Baseball rankings for teams are compiled in various ways by various authorities. Depending on which publication or source you read, you can find different ways of comparing the efficacy and success of various teams. With the overpowering evidence of statistics, however, baseball rankings, in most cases, are compiled according to the same numbers.
During the baseball season, the primary way that baseball rankings are displayed is by the teams' win-loss record. Because only the top four teams in each of the two leagues advance to the fall playoffs, baseball rankings reflect primarily how many games each team wins and loses as compared to the other teams in their divisions. Baseball has two leagues, the American and the National, and each league has three divisions. For each league, the winner of each division and the team with the next-best record overall make it to the playoffs. Baseball rankings show which teams have the best win-loss records throughout the season, so it is not a surprise which teams make it to the playoffs.
Baseball rankings also include the various statistics that make the sport so detail-oriented. One of these statistics is the batting average. A batter's average is how many times he gets a hit in the total number of at-bats he has.
The batter's average is a strict percentage. For example, if a batter gets three hits in ten at-bats, his batting average is .333. Baseball rankings list teams by batting average. It is not always the case that the teams with the highest team batting average advance to the playoffs, but this is a common occurrence.
On the pitching side of the equation is the Earned Run Average (ERA), the number of runs not caused by errors that a pitcher allows for the innings he pitches. The key word in there is errors. If a run scores because of an error, the pitcher is not "charged" for that run. In nearly every case, the lower a pitcher's ERA, the more successful he is.
ERA is calculated in a slightly different way than batting average. The standard is nine innings, which is how long a baseball game usually lasts. If a pitcher gives up one earned run every inning for nine innings, his ERA is 9.00. If he gives up only three runs in nine innings, then his ERA is 3.00. Teams combine their pitchers' ERA for a team ERA, and the team with the lowest collective ERA is at the top of the list. As with batting average, it is generally the case that the teams with the lowest ERA are are those at or near the top of their division.
Nearly every other statistic in baseball lends itself to rankings, both for the individual and for the team. Baseball rankings include categories like hits, runs, doubles, triples, home runs, errors, on-base percentage and defensive fielding percentage. In each of these categories, baseball rankings list teams from best to worst. About the only category that a team doesn't want to lead is errors.