These units are fluid and can change on a daily basis. Each week during the regular season, teams have the opportunity to elevate up to two practice squad players, but players may not be elevated more than three separate weeks during the season without being elevated to the 53-man roster.

While the end of the preseason marks the beginning of the regular season, it also signifies the end of a dream - at least temporarily - for many football players. During the preseason, NFL clubs are able to carry 90 players on their rosters. During the regular season, they are only allowed 53, plus a 16-man practice squad.