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Description of the data topic MLB Roster. This includes the definition as well as the coverage of the data topic or element on the site.
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MLB Roster

Since 2012, TBC has been tracking transactional data for all MLB and Minor League players which allows us to be able to recreate roster history for any of these teams. This includes current rosters as well as rosters on a particular date.

Note that the roster information is fully based on transaction date and that the transaction date may be "around" the time of the transction but not exact and therefore any given roster for any of the team will be close to accurate but not necessarily perfect.

There are 2 types of MLB Rosters. The ACTIVE ROSTER represents the players who are active and available to play in a game at any given moment. Outside of September, teams have a 25-man active roster and are constantly shuffling the roster with callups and injuries throughout the year. A player accrues service time while on the Active Roster, regardless of his playing time.

The 40-MAN ROSTER spans both the active roster and short-term injured players and select minor leaguers. Minor Leaguers on the 40-man can move up to the Major Leagues without restriction, provided they are still in their option years. (First 3 years of service time usually). A player leaving the 40-man roster will be eligible to be claimed by another team. A player joining the 40-man is said to have his contract purchased and this player will usually go straight to the Major Leagues. At no time can a team be above 40 players but they can be under. Minor Leaguers (depending on their experience) will need to be added to the 40-man or risk being lost to other teams in the Rule 5 Draft. This forces teams to allow players to pursue other opportunities for their careers instead of being trapped in an organization.