After David Robertson entered Monday night's game and struck out Wilson Betemit, Mark Reynolds, and Robert Andino through the use of 94% fastballs (16 out of 17 pitches were either a four-seam fastball or a cutter), I began thinking of how truly dominant that is. So far this season, 84.3% of the pitches Robertson has thrown have either been a fastball or a cutter. Batters know what is coming, but he has still struck out an astounding 42.9% of the batters he's faced.
Take a moment to reflect on those percentages. About 84 out of every 100 pitches Robertson throws will be some sort of variation on his fastball. Despite this, he still hasn't given up a run and his K/9 is 14.73. He hasn't come close to regressing from last year's dominance, but somehow, he's improved.
A season ago, David Robertson sported a 1.08 ERA and a 1.84 FIP on his way to a 2.8 WAR season, a very high number for a reliever, especially one who only threw 66 2/3 innings. He also struck out 36.8% of the batters he faced on his way to a 13.5 K/9, the highest mark in the American League among qualified relievers. He had one knock in his game, though, an astronomically high 4.73 BB/9.
This season, through 11 innings, he has a 0.00 ERA, a 0.50 FIP, and has already accumulated 0.6 fWAR. His K/9 and K% have each increased, and amazingly, Robertson has nearly cut his walks in half, down to just 2.45 BB/9. Robertson was already an elite reliever, but the steps taken so far in 2012 have put him on another level.
Essentially, Robertson has been Rivera-esque. Mariano has made a living on manipulating his fastball, and despite knowing that the cutter is on it's way, batters still can't hit it. Robertson has seemingly molded his game after the greatest reliever of all time, working off of his fastball, the majority of which have been cutters.
Admittedly, it's impossible to sustain a 100% left-on-base percentage. No pitcher can last an entire season without allowing a run. But over the last 13 months or so, Robertson has shown that he is among the best pitchers in all of baseball, and to have that kind of insurance coming out of the bullpen must be one hell of a safety net for Joe Girardi.