When the Minnesota Twins drafted University of Louisville closer Nick Burdi in the second round in 2014, many analysts felt that Burdi could reach the majors very quickly and provide a rapid boost for the Minnesota pen. He certainly had classic closer stuff: a non-straight fastball clocked in the upper-90s and hitting 100-101 at times, along with a plus slider. After a difficult freshman year in 2012, he improved his command substantially and was unhittable in 2013 (0.76 ERA, 62/13 K/BB in 36 innings, 16 saves) and 2014 (0.49, 65/10 in 37, 18 saves).
After signing, he posted a 38/10 K/BB in 20 innings with just 13 hits allowed in A-ball. Sufficient command of nasty stuff=quick advancement.
Burdi opened 2015 with Double-A Chattanooga with eyes on Minnesota for the second half but his hopes unraveled quickly. He walked 12 men in his first eight innings, leading to an ERA over 10.00 in April. He suddenly improved in May (15/3 K/BB in 13 innings, 2.03 ERA) but fell apart again in June (9/7 K/BB in nine innings, 8.00 ERA). He was reportedly having trouble keeping his mechanics in gear.
The Twins sent him down to High-A in early July to work on his delivery and right the ship. And indeed he did just that, posting a 23/0 (not a typo) K/BB in his first 16 innings and a 29/3 mark in 20 innings total, 2.25 ERA. Burdi moved back up to Chattanooga this past weekend and the work he put in with Fort Myers seems to have stuck: he threw two innings on Friday night, striking out five and walking nobody.
Now, the first part of the season still counts of course, and Burdi will need to prove that he can maintain his current touch. There's absolutely no doubt about the stuff; his dominance ratios back up the radar guns and scout reports. If his command is even adequate, he'll be a bullpen mainstay, perhaps as soon as next year if his adjustments this year hold together.