The 6'8" 23-year old Volstad was drafted in the 1st round (16th pick) of the 2005 draft out of a Florida high school (Palm Beach Gardens). He made his debut in July of 2008, and finished the year making 14 starts and had a 2.88 ERA, allowing the Marlins to dream that they had yet another young future pitching star. He hasn't been all that spectacular since then, as his career record sits at 19-24 with a 4.40 ERA and 1.39 WHIP. He pitched very well versus the Mets in his two starts in 2008 (12 1/3 innings, only one earned run), but lost both starts in 2009 (11 innings, six earned runs).
Volstad has a great pitcher's body (6'8" 230 pounds) and throws on a down-hill plane straight over the top, but instead of being a power pitcher, he's a finesse pitcher. He throws a sinking fastball 90-93 mph, a tight curve (78 mph) and shows good arm action and sinking movement on his change (84 mph). This year he has also added a slider (85 mph), with mild success. He doesn't rely on swings and misses (5.3%) and is a ground-ball pitcher. He has never struck hitters out (6.6 K/9 even in the minors), but relies on good control (2.4 W/9 in the minors); that has risen to 3.5 W/9 in the majors.
So far this year he's made 15 starts (90 innings), and is 4-7 with a 4.40 ERA and 1.36 WHIP. His strike-out rate is still too low (5.4 K/9), but is doing a good job of continuing to get ground balls (50%+), and minimizing home runs (8 HR in 90 innings). He's gone 6+ innings in 10 of his 15 starts and has allowed 4+ runs in four games. His last start versus the Padres he went six innings, walking none, allowing seven hits and three earned runs, while striking out six.
The future of Volstad is much debated; some still project him as a front-line starter, others see him as having minimal additional upside from what he's currently showing. I'd take my chances on a 6'8" sinker-baller that's only 23 years-old if the Marlins grow weary of him and his lack of strike-outs.