PDO

PDO adds a team's or player's on-ice shooting percentage, how often their shots become goals, and on-ice save percentage, how often opponent shots are stopped while they're on the ice, into a single number. Despite looking like an acronym, it originated from an online commenter's handle rather than standing for specific words.

The formula is PDO = on-ice shooting % + on-ice save %, often expressed on a scale where league-average sums to 100, or 1.000. Because shooting percentage and save percentage both have a large random component over a season, and because the league-wide sum across all teams must converge toward 100 by construction, a team sitting well above or below 100 is often described as due for regression to the mean back toward it.

Analysts use PDO alongside shot-attempt measures such as corsi and fenwick to separate teams that are winning because they control play from teams winning on unsustainable shooting and goaltending variance. The common pitfall is treating all PDO deviation as pure luck: some of the gap reflects real, persistent skill, elite shooters and elite goaltenders do exist, so an extreme PDO is a flag worth investigating, not automatic proof that a team's results are about to reverse.