The official rules are on-line, for anyone who doesn't want to accept someone else's summary. https://registration.mlbpa.org/pdf/MajorLeagueRules.pdf If you go down to Rule 6, which logically enough follows Rule 5, the procedure for removing the player from the major league roster is detailed. There is no mention there of trading. Presumably what teams do, when a trade is desired, is to go through the entire process (mainly the Waiver process), and then the player is returned to the original team in exchange for half the draft price. At that point, the two teams can proceed with a trade (perhaps with the half-price money going back where it came from). As has been said in multiple ways, above, this is somewhat fanciful - a player that no other team wants via waivers probably isn't worth trading for anyway. But it could happen. Oh, and the Cub Reporter site seems to have given a good summary. No quarrel there. It's just, the actual rules aren't really that opaque.