Clayton Kershaw's slider is arguably his best pitch. Fangraphs has it at 22.3 runs above average over the course of his career. He's off to a good start with the pitch this season, as batters have managed one hit on 27 swings. He's also struck out nine batters on sliders and they've put up a 48.1% contact rate overall against them.
Kershaw's fastball has given him a little trouble this season. In his last start in Colorado, Kershaw allowed two home runs on fastballs, and both were pitches up in the zone.
It looks like Kershaw's fastball is coming in a little flatter than in previous seasons. The HRs to Chris Ianetta and Troy Tulowitzki were located in the upper middle portion of the zone and had BrkX readings of under -1.0. Batters have put up an expected wOBA of .323 so far against Kershaw's fastball, compared to his previous three season expected wOBA of .291. But with only two starts worth of fastballs to compare, it's obviously much too early to draw any significant conclusions from the data.