When a radar gun says the pitch is 90 miles per hour at what point in the balls travel to home plate is the radar gun measuring the velocity?
The measurement is made at the point where the ball is when the trigger is squeezed and the contacts close to make active the unit. The gun responds in a "split second" by sending out a pulse, catching the return, and then comparing the two to discover the dissimilarity (the Doppler shift). It is so fast that the ball doesn't travel very far in the time it takes the unit to respond and resolve the speed.