Acceleration measures the time any player on the field takes to reach his Maximum Speed, starting from the point of bat-on-ball contact. It can be applied to a batter, baserunner or defender.
Acceleration is an important tool for providing context to a player's quickness. Obviously speed is important, but if a player doesn't reach that top speed quickly, it loses some of its value.
Watch: Statcast records Mike Trout's Acceleration on a stolen base.
In A Call
"It took him X seconds to reach Maximum Speed"