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 is projected to receive his throw at the center of the base.
When a throw's flight path ends in front of or beyond the base's midpoint, Statcast accounts for the thrown ball's speed and projects how long the throw would have taken to reach the center of the intended base.
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.
Below are the best average pop times to second base on stolen-base attempts (min. 15 SB attempts at 2B) from the 2018 season. The MLB average on steal attempts of second base is 2.01 seconds.
1.90 seconds -- J.T. Realmuto
1.93 seconds -- Yan Gomes
1.94 seconds -- Jorge Alfaro
1.94 seconds -- Austin Hedges
1.94 seconds -- Manny Pina
1.94 seconds -- Gary Sanchez
In A Call
"The throw got to the bag in X seconds"