the server ranking is a pointed based system. every player gets 1000 points to start with. when you kill someone you take x amount of points. someone kills you, they take x amount of points from you.
X in this factor is points
k represents the killer and d represents the dead
if the d has 1500 x and the k has 700. the points taken is higher cause of the point difference. points can be up to 70 and as low as 5. this makes it so the low ranks and quickly recover them selves after a bad night. when a high ranked person kills a lowr rank they only get 5 at the most.
also weapons play a big part in your points. they have multipliers attached to them. ak m4 are 1.25 and awp 1. p90 is i think a 1.75x. nades are 3x and knife is 5x i dont remember all of them. it really isnt easy to be number one cause a couple noobs or new people kill you, you can go down 200 points in one map.
you can have a positive kdr and still lose points depending on who kills you