Jason Stoffel isn't exactly a pitcher with a high ceiling, but a good fastball (which was clocked as high as 96 MPH) and high strikeout rates early in the minors make Stoffel an interesting arm in the Giants minor league system.
Stoffel played college baseball at the University of Arizona (a very good baseball program) where he put together a solid career as a reliever, finishing as the Wildcats' all-time saves leader (He earned 29 saves in three seasons). While his 2008 campaign with the Wildcats (1.71 xERA, 14.8 K/9, 5.3 K/BB ratio) was much better than his 2009 one (2.68 xERA, 9.2 K/9, 2.2 K/BB ratio), Stoffel came into the 2009 MLB Draft as a polished power pitcher who had a closer's mentality and a fast track ticket to the Big Leagues, according to John Klima of Baseball Beginnings.
After being drafted in the fourth round, the Giants assigned him to Rookie League right off the bat. In 9.2 IP, he allowed eight hits and only struck out six batters, but he showed very good control. He faced 38 batters in Arizona and didn't allow a single walk. The good control carried in a promotion to the Northwest League, as he faced 39 batters and pitched 10.1 innings, but only allowed one free pass. Furthermore, Stoffel displayed better command and dominance with the Volcanoes as he struck out 13 hitters and finished with a WHIP of 0.68.
The good campaign in Salem-Keizer earned Stoffel some attention from baseball writers and analysts going into the 2010 season. Baseball America ranked him as the 15th best prospect, and John Sickels had him as the ninth best in the Giants system going into 2010. Stoffel spent his 2010 in San Jose, mostly as the team's primary closer. He didn't disappoint in the role, as he earned 25 saves and helped the Giants win a second-straight California League title.
However, most of his numbers suffered from a bit of an inflation from the previous season (which is probably to be expected since he only pitched 20 innings in 2009). In 50.2 IP, Stoffel had a WHIP of 1.56 and a xERA of 4.66 (which is 18 points better than his 4.84 ERA). He still showcased the power fastball and electric stuff (11.7 K/9), but the pinpoint control he displayed in 2009 faded. He had a BB/9 of 4.3 and a K/BB ratio of 2.75. Also concerning was the fact that he was more hittable in San Jose than in Arizona or Salem-Keizer, as had a 9.8 H/9 in 2010 (almost a three point jump from the previous year). Of course, you could probably point to the high BABIP (.383) and the fact that the California League favors hitters as a reason for the inflation in hits allowed. Thus, while the high rate of base hits was an issue, it didn't alarm too many people.
This year, Stoffel's stock fell a little bit in the eyes of minor league analysts and scouts. Baseball America dropped him to No. 22 in their Giants prospects rankings, and John Sickels dropped him out of the Top 20 all together (though he did list him as a honorable mention). Nonetheless, there was still hope for him, as Rob Gordon in the Minor League Baseball Analyst 2011 annual rated Stoffel as an 8D prospect (the number representing upside and the letter representing possibility of reaching that upside; the higher the number (9 being the best) and letter (A being he's a lock to reach his upside), the better).
This year, there have been a fair share of issues for Stoffel in Richmond. He has pitched 13 innings in the Eastern League so far and has allowed 16 hits and 6 walks, and his ERA is currently 4.85 and his WHIP is 1.69. The biggest concern for Stoffel has been the loss of his dominance and command in comparison to last year, as his K/9 rate is down to 7.6 and his K/BB ratio is 1.83. Considering his MO is as a power reliever who can dominate in the ninth, Stoffel hasn't exactly showed signs of improvement since last year, which doesn't bode well for his Major League hopes. (It's especially concerning since the Eastern League tends to favor pitchers; the positive spin on it though is the fact that he is two years younger than the average EL pitcher, so he has that going for him.)
In reality, there wasn't a huge amount of upside to Stoffel to being with, and he probably is going to always be what he is: a power-armed, one-to-two inning reliever. He is a big guy (six-foot, two-inches, 225 pounds), but he isn't very athletic, and he was pretty much described as a one-pitch pitcher who was destined to the bullpen the second he was drafted. He has been working on his secondary pitches to change that reputation, but it is coming slower than the Giants organization expected/wanted. Here is what Baseball America said about his pitches:
"Stoffel throws his fastball at 88-93 MPH, at times reaching the mid-90's, and has a power slider that sits in the upper 70s and touches 80 MPH. He can turn it into a hard slurve at times. He worked on a changeup on the side, but didn't have the confidence to use it in games. His future depends on his ability to locate his fastball down and to both sides of the plates, something he he's shown the ability to do when he's composed on the mound."
If Stoffel can get his walk and command issues from last year and the beginning of this year under control, and display that K/9 that made him so enticing in San Jose, then he certainly could be contributing to the Giants bullpen in a year or two. As Baseball America implies, the stuff is there and Major-League ready. He just needs to polish up his command, especially as he continues to progress and develop in the Giants system.