On steal or pickoff attempts by a catcher, Pop Time represents the time elapsed from the moment the pitch hits the catcher's mitt to the moment the intended fielder receives his throw.
Pop Time is a combination of a catcher's footwork (getting into throwing position), Exchange (glove to release), and Arm Strength (velocity of throw). Pop Time is a much better assessment of a catcher's ability to throw out baserunners than the strength of his arm alone. A catcher with a great arm isn't going to throw out many baserunners if it takes him a while to transfer the ball to his throwing hand and then release the throw.
A catcher with a good Pop Time doesn't always throw out baserunners, however. A large part of his success is dependent upon the runner's speed, the throw's accuracy and the pitcher's delivery length. But with a quick Pop Time and an accurate throw, a catcher is doing what he can to stop the opposing running game.
Watch: Statcast breaks down Salvador Perez's 2.06 second Pop Time on a throw to second base.
In A Call
"The throw got to the bag in X seconds"