Roster moves made by MLB clubs in August are sometimes made with an eye toward post-season roster eligibility.
With that in mind, here are the 2017 MLB post-season roster eligibility rules:
A club's Active List (25-man roster) must be submitted to the MLB Commissioner prior to the start of the first game of each post-season series (Wild Card game, LDS, LCS, and World Series).
A club's Active List can be changed (tweaked) prior to the start of the first game of each series (WC, LDS, LCS, and WS)
1. A player who received a Prohibited Substance Suspension prior to the start of Spring Training, during Spring Training, during the regular season, or during a post-season series (Wild Card, LDS, LCS, or World Series), is ineligible to play in any MLB or minor league post-season game(s) or series in that season, even if the player has completed serving the suspension.