create the leaderboard, add player X to the board and set its value to variable (int) nKills[]
trigger:
event -
a unit dies
cond -
none
action -
set nKills[Player number of owner of killing unit] = nKills[Player number of owner of killing unit] + 1
set value for player [owner of killing unit] to nKills[Player number of owner of killing unit]
if u need only 1 player then forget the array[] if u want to sort it just use the sort function