The Arizona Diamondbacks named Ian Kennedy their opening day starter for 2011. Kennedy excelled at getting batters to swing at pitches low in the strike zone in 2010, helping him improve his ERA from his time with the Yankees.
The most concentrated area for these pitches is below the strike zone, where even if a batter makes contact, the result for the pitcher is likely to be positive. Kennedy is able to pull this off by using two pitches with similar movement that can trick batters.
The change up represents his predominant pitch for getting low swings:
So Ian gets downward movement in on a left hander with this pitch. He can also release the curve ball, which is even move extreme.
If batters look for the change, Ian can unleash the curve, which falls more and move in on lefties (away from righties) much more than his change up. His two off-speed pitches keep batters guessing, and swinging over the top.