In an organized sports league, a season is the portion of one year in which regulated games of the sport are in session. For example, in Major League Baseball, one season lasts approximately from April through September; in European football (soccer), it is generally from August until May (although in some countries, especially those in Scandinavia, the season starts in the spring and finishes in the autumn due to the weather conditions encountered during the winter). A year can often be broken up into several distinct sections (sometimes themselves called seasons). These are:

Pre-season

Most team sports have a period of training and exhibition games or friendly matches prior to the official start of the season. The games' results have no meaning for the upcoming season, but serve as a way to prepare the players and the team, and sometimes to raise the team profile through lucrative overseas tours.

Regular season

The terms season (UK), regular season (North America) and home and away season (Australia) are used to denote the time when the bulk of games are played. In Australia and North America, it is common for a teams to play a regular season and use the results to seed a playoff tournament (see below). Elsewhere, league and/or cup competitions are played at the same time during the season. Depending on the sport and league, all teams may or may not play against each other. All teams usually play the same number of games, and will play half the matches at their home ground and the other half away at opponent's grounds.

Post-season

main: Playoff

Many sports have playoffs, which generally occur after the regular season is finished. A select number of teams, generally the ones with the best overall records (most wins, fewest losses) from the regular season, enter into a playoff tournament. Each sport may use one of many playoff systems to determine the champion. The teams compete against each other for the top prize of their league.

Off-season

The off-season, vacation time, or close season is the time of year when there is no official competition. Although upper management continues to work, the athletes will take much vacation time off. Also, various events such as drafts, transfers and important off-season free agent signings occur. Generally, most athletes stay in shape during the off-season in preparation for the next season. Certain new rules in the league may be made during this time, and will become enforced during the next regular season.

Seasons by league

Seasons of certain leagues occur usually during these months:

Each color corresponds to a specific sport (leagues of the same sport are colored identically), with months of the year indicated as follows:

• Start of the season denoted by "S"
• Playoff(s)/postseason/knockout stages denoted by "P"
• Final(s) denoted by "F"
• Off-season are denoted with blanks