With the trade deadline having come and gone and teams now being in the middle of the trade waiver season (which ends Aug 31st), I figured it might not be a bad idea to brush up on how the waiver and trade system work at this point. There seems to be some confusion out there as to how this system works, namely that any player put on waivers can simply be claimed. This of course, is too simplistic and not the case.
After the trade deadline (July 31st), teams can still trade players, with an additional step in place. Each team can (and will) put players on waivers right now. First off, don't panic when you hear that Jeff Niemann or Reid Brignac have been placed on waivers. This does not mean that the Rays want to get rid of them. Most players are put on waivers this time of year, and it's basically to gauge interest and return.
Once a player is put on waivers there are a few things that can happen.
1) No one claims the player. If no other team puts a claim in, that player has officially cleared waivers and is free to be traded to any team through the end of the season, though to be added to the playoff roster, you have to be added by Sept 1.
2) One team makes a claim on the player. This has two outcomes. Either the original team can simply allow him (and his salary) to be claimed or they can pull him off waivers and attempt to work out a trade with only that team. This, in my opinion, is why most players are put on waivers, to gauge interest and return. If the player is pulled off of waivers and a trade is completed, the deal takes place. If he is pulled off of waivers and no trade is consummated, that player remains on the original team's roster. He can be put back on waivers, but there are additional rules. A player can only be pulled back off of waivers once. If he is pulled off of waivers and then placed back on waivers, the original team loses it's ability to "save" him by pulling him off waivers again.
3) If multiple teams place a claim on the player, the team with the worst record gets first crack in both the claims process (assuming he isn't pulled back) and in the trade process (assuming he is pulled back). This functions just like the regular waiver wire (worst gets first pick). The worst record is also by league, so if an AL and NL team make a claim on an AL player, the worst record in the AL gets first dibs over the worst record in the NL (even if the NL team's record is worse).
Some other caveats. If a trade is worked out for a "waived" player and the pursuing team wants to trade a player from their 40 man roster, he has to be subjected to the waiver process also.
The waiver period is 48 hours. Although I can't find it stated somewhere (and I'm sure someone can either confirm or deny), I believe that if a player is claimed, the teams have 48 hours to make a deal or the player is remains with the original team and the one free pullback has been used.
Here are some helpful links that possibly summarize this better than I did.
So with trade waiver season in full swing, it's not as easy as hearing that Adam Dunn (or any other player) has been placed on waivers and we can claim him. Not only does our record put us further down the list, but he can still be pulled back with the hopes of a trade being done.
Hope this helped a bit with the trade waiver system.