Clayton Kershaw started the season with 17 strikeouts in 13 innings pitched. He's maintain a high strikeout rate throughout his career, as he uses three main pitches to knock out batters:
While Kershaw's fastball results in a high number of Ks, his curve ball and slider are much more efficient at delivering the punch out. Part of that comes from the change in movement. Kershaw's fastball does not drop as much as expected:
His curve and slider both drop quite a bit:
The curve drops a little more and stays show less lateral movement. The three pitches show a great separation in speed as well. In the following graph, you can see the speed, as well as why each of the pitches is effective (click graph for a larger image):
The slider comes in around 81 miles per hour. Like the fastball, batter do a good job of recognizing the pitch as a strike, but with the good movement, they make contact much less often. The slider is his swing and miss pitch.
The curve ball is the pitch that fools batters in multiple dimensions. They swing a lot less at the curve, and when they do it's less likely to be a strike in the first place. With fewer swings, the curve can be dropped over for a called strike three. While batters make more contact against the curve than against the slider, they make less contact than against the fastball. When batter are swinging at pitches out of the strike zone, even making contact will often result in something good for the defense.
With three pitches capable of getting a batter, Kershaw keeps hitters guessing. Three different speeds and three different movements means lots of strikeouts, and less pressure on the Dodgers defense.