Even though Major League Baseball's July 31 non-waiver trade deadline has passed, there will likely still be a number of players dealt before the end of the season. Teams can still make trades over the next few weeks, but the rules are not as simple.
Starting on August 1, each club can place a player on waivers. Any player that can potentially be dealt could be placed on waivers, and if the player is claimed, the organization can pull the player back without losing the player. If a player is not traded within 48 hours, however, he can be dealt to any major league club during the month of August.
Several teams can put in a claim on the same player although there is only one club that has priority with regard to discussing a trade for the player. Priority is given to the organization with the lowest winning percentage in the same league -- it ranges from worst to first and subsequently worst to first in the other league.
Although most teams would only put in a claim if they are sincerely interested in acquiring a player, some clubs do so to prevent rival organizations from acquiring a key major league piece while trying to make a playoff push. The club that puts in a claim is then obligated to take on that player's entire contract. The player's club could lose the player but not pull him off of waivers.
There is not much of a risk to putting a player on waivers and many organizations do so in order to gauge interest and get a sense of the market and how valuable their players are. Most players tend to clear waivers, and more often than not, clubs do not put in claims to disrupt the plans of rival organizations. A team that claims an unwanted player might have a desired player claimed before it had the opportunity to do so in the future.
After August 31, all waivers expire. A player has to once again clear waivers before a trade becomes realistic, however players added in September are not eligible to play in the postseason.
Dan Haren, if he was not dealt, was a candidate to be traded in August. However, after he was traded to the Cubs, the Marlins might place several bullpen pieces such as Mike Dunn and Bryan Morris on waivers. Each time a player is placed on waivers, it is not always made clear. As a result, teams can get a sense of value without making it clear they are considering moving a certain player.