July 31st is often referred to in baseball circles as simply "the trade deadline". The more accurate term is "the non waiver trade deadline". After July 31st, baseball clubs can still make trades. As Kurt Mensching wrote in his column for the Detroit News, plenty of August deals happen every season, and the Tigers have been very active in August in recent years.
For example, in 2006, the Tigers acquired infielder Neifi Perez from the Chicago Cubs for minor league catcher Chris Robinson. In 2008, they signed pitcher Freddy Garcia to a minor league contract and later called him up to pitch. In 2009, Aubrey Huff was acquired in August. In 2011, it was Delmon Young who was acquired from the Twins. In 2012, they acquired utility man Jeff Baker from the Cubs.
The selection of available players to trade for is not as great in August as it is in July. The main difference is that after July 31st, a player must either clear waivers, or be traded to the club who puts in the priority waiver claim before his contract can be moved.
The process works like this:
Starting August 1st, clubs can put players on "special waivers", also known as "recallable waivers". Any player who could possibly traded can be put on waivers and if they’re claimed, the club can call them back without losing the player.
If a player is not claimed within the waiver period, he can be traded to any MLB team during the month of August. If multiple teams put in claims on the same player, only one club can have the priority waiver claim. Priority is given to the team with the lowest winning percentage in the same league, from worst to first, and then from worst to first in the other league.
There is a protocol whereby clubs generally do not put in a waiver claim unless they are genuinely interested in a player, or in a few rare cases, they want to block a rival team from being able to acquire the player. However, the club that puts in a claim should be prepared to take on the full contract of the player, because that player’s current club can just let the player go if they don't recall him off waivers.
A club that is not a contender has no reason to block another club from acquiring a player, but a non contender might want to put in a claim on a player who is under contract in future seasons. Kenny Williams, when he was GM of the White Sox claimed Alex Rios from the Blue Jays, and Toronto just (wisely) let him go. Chicago took on the whole contract and has been over paying Rios ever since.
The Red Sox and Yankees, in particular, are known to have played the blocking game, but that can often impact other clubs, and not just the two of them. As an example, say the Red Sox, Indians and the Tigers were all looking for bullpen help (they were all talking about Javier Lopez until the deadline struck). Let’s say that the Mariners put a good relief pitcher on special waivers, (Oh, maybe Oliver Perez) and the Tigers are interested.
The Yankees might want to block the Red Sox from being able to trade for a relief pitcher, so they start claiming all the good relief pitchers who are placed on waivers. Since the Yankees have a lower winning percentage than the Tigers, Detroit might never get a shot to put in a claim on a relief pitcher. Or the Indians might put in a claim,. and the Tigers never get a shot at that player.
Dave Dombrowski made a specific reference to the August rules in his press conference announcing the acquisition of Jose Iglesias from Boston. He plainly stated that he felt that the chances of getting a good shortstop through waivers to the Tigers' position in August were very remote. He might get a Brendan Ryan from Seattle, but not a player like Iglesias, who could help a team for years to come.
The list of players who are placed on waivers every August is quite an impressive list, since there is no risk to putting a player on recallable waivers. Clubs will often put almost their entire roster on waivers, hoping that the player(s) they might trade will sneak through with the pack. The vast majority of players clear waivers. Clubs don’t want to put in claims, disrupting the plans of another club, for fear of retaliation either that season or in another season when they’d like to get a player through. The protocol is "you let this guy through for me and I’ll let that guy through for you".
Special waivers could also be referred to as secret waivers, because MLB does not publish the list of players who are placed on waivers. Quite often, information leaks out, and sometimes that information is intentionally leaked for one reason or another. All clubs have access to the full list of players who are placed on special waivers.
So, what players might be available in August? Well, any player could clear waivers, but the most likely candidates are those who have contracts that their current clubs would like to be rid of. Players on non contending clubs who are due to become free agents after this season are the obvious candidates.
That list includes Twins outfielder Josh Willingham, Seattle outfielder Raul Ibanez, Milwaukee Brewers' 3B Aramis Ramirez, and Angels pitchers Ryan Madson and Jason Vargas. Willingham has one year left on his contract at a reasonable $ 7 million, and the others are set to be free agents after this season. Willingham, Ramirez, and Madson are currently on the disabled list, and would only be traded if they prove to be healthy.
Also, players who are simply not worth their current salaries, on any team are candidates to be traded. I'd put the White Sox Alex Rios, the Giants Tim Lincecum, and half the roster of the New York Yankees on that list. Those players could clear waivers, because nobody wants to pay their current salaries.
Good players on National league teams are less likely to make it through waivers to the Tigers, who would be in the 27th waiver position as of today. The Tigers have a better shot at players in the American League, although the Indians and Yankees would have the priority waiver claim, and both could also use bullpen help. Waiver claims can not be traded, so teams at the top of the pecking order can’t have teams lower down the list put in a claim for them. The player can’t then be moved to another team without going through waivers again.
One caveat is that a player can only be recalled once during the month. If a team puts a player on waivers, and a claim is made and they recall the player, the next time that they put the player on special waivers, they can’t recall him.
After August 31st, all waivers expire, a new waiver period begins, and any player must again clear waivers before they can be traded. However, players who are traded in September are not eligible for post season play.