Quantified Shot Quality (qSQ) is metric developed by using Second Spectrum video tracking data.
In brief, qSQ is the effective field-goal percentage when the type and location of the shot and nearby defenders have taken into account.
Before video tracking technologies, effective field goal percentage was the most advanced metric to evaluate a shooter. What Second Spectrum does is to process some big amount of data (trajectory of the ball and the players on the court throughout the game) by employing machine learning that leads to better evaluate player performance.
Quantified shot quality is the likelihood of a “field goal attempt” turns out to be a “field goal made” after factors such as velocity of the shooter, the closest defender, the next closest defender, position, distance, and others are taken into account. The higher the qSQ, the easier (in terms of distance-being contested or not at the other factors explained) the shoot is. See also Quantified Shooter Impact metric.