Steve Edlefsen to me is one of those "under the radar" arms that has done well in the minors despite low expectations. Drafted in the 16th round of the 2007 MLB Draft by the San Francisco Giants, Edlefsen came out of Nebraska after only really pitching full-time for one year. After transferring from Barton Community College (he underwent Tommy John surgery in 2005, missing his entire sophomore season), he was originally a utility infielder primarily, batting .260 with a .695 OPS in 70 AB his junior year. His senior year, he was mostly used in a relief role, as he pitched 26.1 innings and struck out 25 and walked 27, producing an ERA of 4.10 and a WHIP of 1.82.
Nonetheless, the Giants took a waiver on him despite his lack of innings in college (probably not a bad thing since his arm didn't have too many miles on it) and he hasn't disappointed. In Salem-Keizer in 2007, he pitched 33.1 IP and posted an ERA of 1.62, a WHIP of 0.90 and a 7.0 K/9. His K/BB ratio and FIP weren't exactly impressive (1.60 and 3.35, respectively), but it was certainly a surprise considering he didn't "wow" anybody his senior year with the Huskers.
In 2008, Edlefsen showed some more improvement, pitching 77.2 Innings and posting an ERA of 3.36, a WHIP of 1.40 and a K/9 of 8.9. The hits increased (8.9 H/9), but his slight improvement in his K/BB ratio (2.03) over more innings pitched (44.1 specifically) was a promising sign that his tenure int the Northwest League wasn't just a fluke.
His third year in the minors proved to be huge in Edlefsen's development. He played at three levels in 2009, starting the year in San Jose and finishing in Fresno. On a stacked San Jose team, Edlefsen dominated, posting an ERA of 0.96, a FIP of 2.20 and a K/9 of 12.9 in 28 innings pitched. He was promoted to Connecticut midway through the year, and while he regressed a little (11.1 IP, 10 hits allowed, 1.00 K/BB ratio) in the Eastern League, he still showed enough for the Giants organization to promote him to Fresno. With the Grizzlies, he finished the year strong, striking out 24 in 30 innings pitched, and sported an ERA of 2.40.
His second year in Fresno proved to be better than the last, as he pitched 64.1 IP, had an ERA of 2.38, a K/9 of 7.0 and earned a spot on the PCL All-Star team as well. Additionally, the good year in Fresno earned Edlefsen a spot on the Giants 40-man roster this Spring. Edlefsen is struggling his third go-around in the Pacific Coast League this year (4.70 ERA, 1.50 WHIP, 11.7 H/9), but he does have a BB/9 of 1.8 and a K/BB ratio of 3.67, all career bests.
Edlefsen is known for his slider and his sidearm delivery (in a post by Bay City Ball, Edlefsen's slider was graded as the best slider in the Giants system in 2007). However, control has been an issue, as his BB/9 in the minors is 4.4 and his K/BB ratio is 1.84. Furthermore, his FIP numbers have been pretty pedestrian over his professional career. Sans the 2009 California League campaign and this year, he has never had a FIP under 3.35, and that was his first year in Salem-Keizer.
He may not be an "elite" prospect by any means (though he was an honorable mention on John Sickels' Top-20 prospect list this year). That being said, Edlefsen could have a good career in the Majors as a middle reliever or perhaps even as a setup man. His slider and arm slot could give Major League hitters problems (similar to Javier Lopez). While the Giants bullpen is set as of now (I don't see Edlefsen replacing anybody at this point), he could be a solid option this year if somebody gets injured, or next year when some relievers become free agents (Guillermo Mota and Lopez will be free agents next year). If he can get his walk issues under control (and he's starting show some progress this year, though the hits allowed is a little discouraging), he could be a guy Giants fans may need to pay attention to in the near future.