What is this? A Statcast metric designed to express the skill of baserunners in advancing via stolen bases.
How this works: Each steal opportunity, sortable between attempts for 2B, 3B or All (combining attempts for 2B and 3B), is assigned a probability of being successful or not, based on the pitcher and catcher the basestealer is running against.
All of a basestealer's attempts -- both successful (stolen bases and advances via balk) and unsuccessful (caught stealings and pickoffs) -- are combined to show his overall basestealing impact, positive or negative.
How to read it: Runner Base Advances Gained is the difference between a basestealer's advances via stolen bases/balks (vs. average) and outs made via caught stealings/pickoffs (vs. average). Runner Stealing Runs is a translation of that to a run value, where an advance is worth +0.2 runs for the runner and an out is worth -0.45 runs; opportunities where a runner did not attempt to run are valued on a sliding scale based on the situation. Lead Distance Gained expresses the distance gained by the basestealer between the pitcher’s first move and pitch release.
Minimum qualifiers: To be qualified, a baserunner must have at least one stolen base opportunity per team game. A "stolen base opportunity" for second base is defined as a pitch thrown with the runner on first, and no other runners on. A stolen base opportunity for third base is defined as a pitch thrown with the runner on second, and no runner on third.
