These stats display how many enemies/teammates each rank on average blinds with every flashbang they throw, the maximum possible number being 5 enemies/teammates. This is an indication of how efficient you are with your flashbangs. Only includes people that were really flashed, not people who for example turned their back to the flash. (i.e. half-blind)
To calculate this we count the total amount of enemies/teammates you flashed for a duration of more than 1.1 sec (in order to exclude half-blind enemies). The sum is then divided by the total number of flashbangs thrown.