During the off-season, teams may have no more than thirty-four (34) players on their active roster. There is no classification limit for the off-season roster. Players signed out of the California Winter League or selected in the Frontier League Draft are exempt from the 34-player limit.
The Sunday prior to Opening Day (May 6 for the 2018 season), teams must be down to 28 players.
Regular season and playoff club rosters will be composed of a minimum of 22 active players and a maximum of 24 active players.
Each club must carry a minimum of twelve (12) rookies (combination of R1 and R2 players) with no professional experience other than specified below and may carry a maximum of twelve (12) players with unlimited professional experience during the regular season and playoffs.
No player or player/coach may have attained twenty-seven (27) years of age prior to January 1 of that playing season.
For the 2018 season, players must have been born on or after January 1, 1991 to be eligible.
Players without prior affiliated baseball (MiLB) experience must be at least 18 years old to play in the Frontier League.
Rookie Classification: The Rookie classification will be split into two sub-classifications, Rookie-1 and Rookie-2. The Rookie-1 sub-classification will be for players who made their professional debut in the current season and therefore have no prior professional experience, or whose experience does not meet the minimum appearances listed below. The Rookie-2 sub-classification is for players who have one year of professional experience.
Minimum Appearance Exception: A player must have accrued a minimum of 50 at bats, 10 games pitched, or 20 innings pitched in a season for that season to count toward the classifications.
Experienced Classification: The Experienced classification is for all players who do not meet the requirements to be classified under the Rookie-1 or Rookie-2 classifications.
21-year Old Exemption: Any player who is twenty-one (21) years of age or younger on or after January 1st of any season and is entering his first year in the Frontier League, regardless of any prior professional baseball experience, will be considered no higher than a Rookie-2 by Frontier League Rules. For the 2018 season, a birthdate of January 1, 1996 will be the cutoff to qualify under this provision.
Military Exemption: Players who have served on active military duty will receive an exemption to the age limit of one year for each year of active duty that was served.
Position Change Exemption: Starting with the 2016 season, position players who are switching to pitching and pitchers who are switching to playing a position will have their classifications reset to Rookie-2 provided that they do not appear in any games at their previous position (batting/running or pitching, depending on the switch).