A Bolt is any run where the Sprint Speed (defined as "feet per second in a player's fastest one-second window") of the runner is at least 30 ft/sec.
Players' Bolt totals for each season are displayed on the Sprint Speed leaderboard. It is a cumulative stat, unlike Sprint Speed.
Billy Hamilton finished first or second in Bolts in each of the first four seasons in Statcast history. Trea Turner ranked first in 2018, with 145 Bolts -- 43 more than any other player -- though he ranked fourth on the Sprint Speed leaderboard (min. 10 competitive runs).
Since Statcast was implemented Major League-wide in 2015, the number of Bolts per season typically has been similar to the number of stolen bases. For example, there were 2,377 Bolts and 2,474 steals in 2018.
Watch: Billy Hamilton registers a Sprint Speed of 30.1 ft/sec on a triple, tallying a Bolt.