The general response of "Who?" is appropriate here, because that's exactly what I said, too.
Balester had a 4.54 ERA in 2011 with the Nationals, alongside a 3.86 xFIP, 8.58 K/9 and 3.53 BB/9 in 35.2 innings. For his career, all with Washington, he has a 4.49 xFIP, 7.11 K/9 and 3.61 BB/9 in 51 innings. (Stats at Fangraphs)
In a release, Tigers GM Dave Dombrowski said:
"Acquiring Collin Balester from the Nationals today adds another good arm to our organization. He has shown the ability to pitch multiple innings out of the bullpen in the past, a role we are looking for him to fill for our club in 2012."
Perry had been a bit of a disappointment since joining the Tigers. This season he had a 5.35 ERA (5.22 xFIP) with a career low 5.84 K/9 and career-high 5.11 BB/9.
This just might be one of those "change of scenery" deals for both players. Also, with innings seven through nine shored up with Octavio Dotel, Joaquin Benoit and Jose Valverde, along with Al Alburquerque to be deployed as needed, Perry's role on the club had greatly diminished. The Tigers will need to carry a long relief pitcher on the roster, and that obviously wasn't going to be Perry. So there was nowhere to stash him but Toledo.
I consulted Texas Leaguers and Fangraphs to get a sketch of Balester. Remember PitchF/X data isn't perfect, but it's more than we knew before. In 2011, Balester used two pitches: a fastball and a curve. The fastball averaged 93.9 miles per hour, while the curve came in at 80. It appears he had a changeup in previous seasons that he shelved when he became a full time reliever.
That move to reliever appears to have been beneficial. His strikeout rate improved greatly as his fastball added some pep.
The area of concern -- in some ways -- is that Balester gives up a rather high percentage of home runs. In the past three seasons, starting with 2011, he's had a HR per fly ball rate of 16.7%, 14.3% and 21.3%. Some of that might be the fault of his home ballpark, which was slightly home run friendly in 2011 and neutral in 2010. As well, you don't want to make too much of splits in such limited innings, either. I would still expect his rate to improve in Detroit, at least over the 2011 numbers.
Balester will take over the long relief role, MLB.com's Jason Beck reported on Twitter.