Pitch speeds are typically those measured by a radar gun. Although radar guns are considered to measure the speed at release, which is the maximum speed, they really don't do so. Doppler radars operate by sending out two pulses and then in effect measure the average velocity the ball was traveling between those two pulses. A gun which sends out the pulses at a higher frequency will register a slightly higher velocity.
There are also guns that will continue to measure the speed throughout the pitch, giving both "out of hand" readings and "at the plate" readings.