A new player has 1000 points. Every time you make a kill, you gain a certain amount of points depending on a) the victim's points rating, and b) the weapon you used. If you kill someone with a higher points rating than you, then you gain more points than if you kill someone with a lower points rating than you. Therefore, killing newbies will not get you as far as killing the #1 player. And if you kill someone with your knife, you gain more points than if you kill them with a rifle, for example.
When you are killed, you lose a certain amount of points, which again depends on the points rating of your killer and the weapon they used (you don't lose as many points for being killed by the #1 player with a rifle than you do for being killed by a low ranked player with a knife). This makes moving up the rankings easier, but makes staying in the top spots harder.
I got this from the HELP screen on the hlstats page..
I cant find an actual breakdown of the point system anywhere, I was curious how it worked too, but that was the only explanation available.
