A coworker sent me this article from SBNation. It basically covers a theory developed Perry Husband that tries to explain why low velocity pitchers, such as Koji Uehara, are effective.
Anyway, I thought it was rather interesting.
Effective Velocity is made up of six tenets, some of which are commonsense and already utilized by successful pitchers at the game's highest levels, others so complex that even major league coaches have difficulty grasping them. It starts with the idea that all pitches are not equal — even those that appear to be identical on the radar gun.
It hinges on response time. Husband's model is based on the arc of hitters' swings, and the understanding that bats must move farther to reach pitches on the inner part of the plate than on the outside edge. Put another way, a batter can hit an outside fastball as it crosses the plate, but to make solid contact with an inside fastball, he must reach it much sooner — up to 2 feet in front of the plate — which requires the hitter to move the bat a greater distance in less time. With this detail in mind, it makes sense to build an approach based not on a pitch's radar speed, but how quickly the man standing in the batter's box can react to it.
This is the basis for the "effective" portion of Effective Velocity.
EV breaks the strike zone into nine regions, each having a different effect on how hitters perceive a given pitch. Based on a hitter's need to reach pitches close to his body more quickly, Husband calculated that reaction time to a 90-mile-per-hour pitch is closer to that of a 93-mph pitch if it runs inside (96 if it's high and tight), and drops to 87 mph if it's placed on the outside edge of the plate (85 if it's low and away).
There is an imaginary stripe that runs diagonally across the strike zone, from the batter's feet to shoulder level in the opposite batter's box, where a pitch's EV equals its actual speed. Husband calls this the Zero Line. He calculated that for every 6 inches the ball moves closer to the hitter from that line, it picks up 2.75 EV mph; for every 6 inches it moves away, it loses an equivalent amount. This gives strikes thrown at identical speeds on a given horizontal plane about a 6-mph fluctuation in reactionary speed from one end of the strike zone to the other. Add vertical differences into the equation and that spread can easily double, all for pitches that are thrown at the same actual speed.
Anyway, I thought it was rather interesting.