Nippon Professional Baseball (NPB) Posting System
There are two Japanese major leagues, the Pacific League and the Central League. Together they are known as "Nippon Professional Baseball" (or "NPB").
A Japanese player who is not under contract to an NPB club can sign with any MLB club.
A player who is under contract to an NPB club may ask his club for permission to sign with an MLB club anytime during a four-month period extending from November 1st to March 1st. If the NPB club agrees to the request, the player is said to be "posted," and MLB clubs have four business days to decide whether to extend a transfer fee offer to the player's NPB club. The transfer fee offers are delivered to the MLB Commissioner in the form of sealed bids.
Once the auction has been closed, the MLB Commissioner notifies the NPB club whether any bids were received, and if so, the amount of the highest bid, but not the identity of the MLB club that submitted it. The NPB club then has four business days to decide whether to accept the bid. The MLB club that submits the highest bid is the only club that can sign the player, and that's only if the player's NPB club accepts the bid.
If no bids are received, or if bids are received but the NPB club rejects the highest one, the player remains with the NPB club and cannot be posted again until November 1st.
If the NPB club accepts the bid, the MLB club that submitted it is awarded exclusive negotiating rights with the player for 30 days. If the MLB club signs the posted player, the NPB club receives the transfer fee from the MLB club. If the MLB club does not sign the posted player within 30 days, the MLB club retains the transfer fee, and the player cannot be posted again until November 1st.