Andrew Cashner took on the role of a starter for the first time in his career with the San Diego Padres in 2013, establishing himself as the rotation's undisputed ace in finishing with a staff-best 3.04 ERA and career-best 1.13 WHIP. How he arrived at those numbers was a product of an impressive second-half stint, posting a 2.14 ERA and 0.95 WHIP over 11 starts following a 3.81 ERA and 1.27 WHIP prior to the All Star break.
How Cashner lowered his walks, hits and earned run average so significantly in the second half of the season stemmed from the development of his slider. By 'development', I am referring to the fact that he was able to adjust and improve his command of the pitch, throw it more frequently and induce a whole lot more swings and misses with it.
Prior to the All-Star break, Cashner's slider was his third pitch, throwing it at a 14.2% frequency, behind his fastball (62.5%) and changeup (23.3%). As we can see, Cashner's location was erratic (18.6% called strike rate) and much too over the plate, which opponents capitalized off of through a .176 well-hit average that was well above the .155 league average against sliders. This hindered his ability to generate swings and misses, too, evidenced by a 17.1% whiff rate that was significantly lower than the league average of 32.2%.
Cashner's 11 post-All Star break starts yielded different results, and it's easy to see why. Firstly, Cashner's slider became his No. 2 pitch, throwing it at a 21.9% rate. It also helped that he was able to stray away from the middle of the plate with the offering, commanding it low and away to right-handed hitters en route to a 21.6% called-strike rate. Consequently, opponents were unable to place quality contact on the pitch (.152 WHAV) and whiffed at a 36.3% rate -- an 18.7% increase from before the break. Yes, that is only slightly higher than the 32.2% league average, but such an increase is nonetheless noteworthy.
While Cashner may still be heavily dependent on his upper-90s fastball -- he threw it 61.7% of the time last season compared to the 47.3% league average -- the second half of 2013 proved his slider has improved leaps and bounds from where it was at the beginning of the season. If he continues to command it with consistency, it will be an effective compliment to his overpowering fastball, potentially enough to make him an elite starter in 2014.