Its the point system. You gain points when you kill somebody ( most likely 5 points, but when they have a high bounty it'll be more ) And you lose points from getting killed. You also gain 50 points for winning the game in a 24 player server and 100 points in a 48 player server. So, if you see a person with a high bounty he'll most likely play alot or is very good at killing players / winning. You can also spend your own point to set a extra bounty on somebody but the bounty u set on somebody will be distracted from your total bounty, You can only do this in spectator mode ( /bounty [username] [amount] )