Ratios are basic expressions of how well players perform. It is simply a measurement of how many successful puck-possession plays a player makes for every 1 unsuccessful puck-possession play. A successful or unsuccessful event could be anything from a completed pass to a lost puck-battle. Simply put, the higher a player's ratio, the more that player helps his team maintain or acquire possession of the puck.
Defensive-zone risk/reward rating is calculated by subtracting the total
number of unsuccessful plays a player makes per-minute of ice-time from
the total number of successful plays a player makes per-minute of
ice-time. Only those events taking place in the defensive-zone are
included. The higher the number the better a player performed.