Last week, the team at Baseball Prospectus unveiled a host of new pitching metrics. The new data attempts to quantify certain concepts like command, control, and deception in a more concrete way. I’d highly encourage you to read through BP’s analysis to get a full scope of what these numbers illustrate.
In short, BP has devised called strike probability, or CS Prob, as a measure of control. CS Prob represents the probability any given pitch a particular pitcher throws will be a strike, adjusted for count, batter, and the strike zone actually called by umpires (as opposed to the rule book strike zone).