The 5-day period following the end of the World Series
Exclusive signing period. Although the day after the Series wraps up marks the official start of free agency, the Basic Agreement — the extensive collective bargaining deal that prescribes the players' terms and conditions of employment — prohibits free agents from signing with any club other than the last one they played for until the fifth day following the Fall Classic's end.
Royal free agents are Zack Greinke, Brad Keller and Matt Duffy. Greinke may or may not retire, and Kansas City shouldn't pursue Keller or Duffy.
Qualifying offers. It's also during this five-day span that clubs can, if they so choose, extend Qualifying Offers to certain of their free agents. A QO gives a free agent the chance to return to his team for one year at a set, MLB-wide amount, which this offseason is anticipated to be more than $20 million. If a player rejects a QO, any team that signs him can lose a draft pick, and the team losing him gets an extra draft pick.
Players are eligible for QOs only if they rostered with the offering team for the whole 2023 season and they've never before received a QO. For example, potential KC free agent Zack Greinke is in the same position this winter as he was last — because he received an offer before, the Royals can't give him one.
QO recipients have 10 days to decide what to do.
Options. That five-day post-Series period is also the only time players, clubs, or both can exercise contract options, which if triggered require players to return to their teams for a contractually-prescribed term. Some contracts give only the player the right to exercise the option, others reserve that right to the team only, and still others include so-called mutual options that allow a player's return only if both sides exercise them, effectively giving player or club a veto.
Some additional important dates...