Moving Saunders is indeed the right move at this time for Arizona, for one obvious reason that Rosenthal himself mentions: Prospect Trevor Bauer is tearing up the minor leagues, and the Diamondbacks should make a move to get him into the majors.
However, beyond that, many teams are going to want starting pitching help at the deadline. Whether because of injury or ineffectiveness, the fact is that many teams need more pitching if they want to bolster their chances for playoff runs.
Saunders is definitely a serviceable middle-of-the-rotation option. He is sitting at a 3-4 with a 3.65 ERA, but his value will be enhanced further by the desperation alluded to above.
In that sense, this would be a very favorable trade for the Diamondbacks. They get to clear the way for a highly touted prospect, and in return for doing that, they will probably get a better return than Saunders would normally receive.
Now, from the other perspective, what teams would be interested in Joe Sanders?
One that jumps out immediately would be the St. Louis Cardinals. With Chris Carpenter out and the recent injury to Jamie Garcia, they could very well be in need (although in the video linked to above, Rosenthal says that they are waiting before making a move).
Another very interesting option could be Pittsburgh Pirates. Their pitching staff has been fine this year, but adding a veteran arm like Saunders could very well help them stay in contention. He is a proven veteran who could provide stability.
Wherever Saunders goes, there is a lot of motivation for the Diamondbacks to send him packing.
It isn't because he is a bad pitcher; moving him simply creates much more value than keeping him in the rotation.
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