Teams have to pass players through revocable waivers to trade them after the July 31st non-waiver trade deadline. Those revocable waivers last 47 hours.
Players who go unclaimed after those 47 hours are eligible to be traded to any team for the rest of the season.
A team has three options if one of its players is claimed off revocable waivers. That team can either pull the player back without penalty, work out a trade with the claiming team, or simply hand the player and his salary over for nothing. Recent examples of this include the White Sox’s acquisition of Alex Rios and the Giants’ acquisition of Cody Ross.
Teams will often put most of their players on waivers to determine interest. There’s no risk in doing so, as they don’t have to actually give up a player that is claimed by another team.
Regardless of the day of the week (Saturday and Sunday are treated as normal days), clubs have two days (48.5 hours) to deal claimed players. They can only negotiate a trade with the team that was awarded the claim on that player.
If only one team claims a player, he can only be dealt to that team. If more than one team claims a player, he can only be traded to the claiming team with the highest waiver priority. The order of priority goes: 1) from worst record to best record among teams in the same league as the club seeking waivers; and then 2) from worst to best among teams in the other league. (In other words, if a player is put on waivers by an AL team, first priority goes to the AL club with the worst record, with the NL club with the worst record in line behind the best AL team.)
If a team places a player on waivers a second time after pulling him back, the waivers are no longer revocable. A claiming team would be awarded the player at that point. Obviously, the risk in placing a player on waivers a second time is significant.
Teams cannot pass players on the disabled list through waivers. If a player is placed on waivers and then placed on the disabled list the next day, his team must cancel the waiver request.
Players acquired after August 31st can’t play in the postseason.