KDR is the amount of kills you have to the amount of deaths you received. In War Games, deaths are only added to your KDR when a player actually kills you rather than every time you die. KDR was added in War Games version 1.13.
The more kills you get, the higher your KDR has, the more times players kill you, the lower your KDR is. For example a KDR of 20 means you get 20x of kills as deaths. a KDR of 0.1 means your deaths are 10x more than the players you've killed.
To the left is a KDR leaderboard that records the highest War Games KDRs.