Bukkit

What is the enhancement in mind? How should it look and feel?
Add Elo rating system to KillStats.
Please provide any additional information below.

Elo is a simple rating system (developed for chess matches, but also used in for example League of Legends or Counter Strike) - in simple words the better player you kill the more points you get.

It would require adding another column to the pvpstats table called 'elo' where the player rating is saved.
Every new player starts with a rating of 1500 (configurable), and the maximum change after killing someone is 16 (configurable).
You can check how it works here http://www.3dkingdoms.com/chess/elo.htm (the maximum change "K" is set by default to 32 in this example)

A has 1500elo and kills B 1500elo -> A has not 1516, B has 1484
A has 2000elo and kills B 1000elo -> A has 2000 because he was far superior, and B still has 1000elo

The formula can be found here http://en.wikipedia.org/wiki/Elo_rating_system#Mathematical_details