Arm Strength is defined as the maximum velocity of any throw made by a fielder -- with the max velocity always being at the release point, due to physics. It can be used to evaluate outfielders on attempted assists, catchers on stolen base and pickoff throws, and infielders on throws across the diamond. Fielders -- especially outfielders -- often get a running start before throwing. As a result, the velocity on their throws can exceed that of pitchers, who throw to batters from the mound.
Putting a quantifiable number on the strength of a fielder's arm helps to evaluate the effectiveness of that arm. However, Arm Strength is not the only component of a good throw. Along with velocity, the accuracy of the throw is very important, as is the trajectory. A 90 mph throw from the outfield that bounces three times will inevitably lose speed each time it hits the ground.
Watch: Statcast records the Arm Strength of Bryce Harper and Michael A. Taylor on several throws from the outfield.
In A Call
"throw velocity," "He made a X mph throw"