Each player gets ranking points calculated for them like is shown in the link Ooper posted for the player Vio.Scarz. Then, I presume, the list of all players are sorted high to low by their total ranking points so the player with the highest amount of points is listed as #1.
Currently, however, it is almost meaningless to pay attention to Ranking because there are numerous strong players with many aliases whose stats have not been combined yet. This skews the results a lot. So, above average and lower skilled players will have a much lower ranking than they actually deserve.
I will make a post to let everyone know whenever I get around to fixing this issue, along with a few other utstats issues, and re-importing all the stats.
