Jered Weaver received a large raise on Thursday thanks to his ability to fool batters with his off-speed pitches. The following graph shows how results vary by speed for the younger Weaver:
This chart drives home the point that major league hitters can handle a fastball. Note that the contact rate is high on his fastball, and at his most common velocity, batters hit it pretty well.
The 78-80 MPH range is where Weaver makes his money, however. Batters are more likely to swing at the pitch, and miss if they do. They also make more outs when they put the ball in play. Weaver throws both a changeup and slider at this speed, with very different movement. His change moves much like his fastball, toward a left-handed batter with a normal downward drop:
Weaver throws a changeup that looks like his fastball, so batters chase that. Over the last three years they've hit .219 off the change versus .246 off the fastball. If they get a feel for the speed of the changeup, Weaver can drop in the slider and fool them with movement, as batters hit just .190 off that pitch. The slider is his most devasting pitch, as you can in the wOBA:
There's nothing wrong with Jered's fastball. A .333 wOBA means the league hits about average against him. That pitch sets up his great ones, and batters look replacement level against Weaver's off-speed offerings.