Perhaps you could make it more expensive to farm prizes. Lets say each player has a global red score, as well as a global blue score.

• When a player gains red score you will also loose the same amount of blue score (minimum is 0).
• When a player kills a player in the same team he looses a score of the same color.
• When a player kills a enemy he will gain a basic score in addition to bonus, based on the enemy players level.

These rules might prevent players from toggling back and forth between blue and red. It will be more profitable to stay invested in one color all the time.

The other problem was the farming games where the player creates games and plays to harvest score. To make it more expensive to farm like this you could add a multiplier that stacks up if the player is moving/jumping or doing some other action while getting shot, while getting almost nothing if the player is standing still.

A third method is to add a multiplier that reduces score depending on how many times you have killed a certain player. So first time you get 100% of score, next time 100%*0.8 = 80% and so forth. If you have killed a player 20 times you will get close to nothing in bonus.

These rules are quite complicated, but at their core they are based on bonuses and multipliers. The more active the players are and the more dedicated they are to a certain color/fraction the more bonus they will get.

I once occasionally watched people inside a MMO use a PvP arena a few times, which gave points for participating and more for winning.

At first it was all fun with 20 vs 20 or however many(dont remember the exact number) fighting, but then the farming started and people wanting to use it as intended found often they were in a team with lazy afk people who only clicked to enter and once after the match to grab points, later dual-cliented afk accounts from people playing at the other side. Then it got so bad normal people would have no more chance of winning cause of rigged matches when they landed in the team with the afk people and stopped going to the arena cause of no more fun. Later again it got even worse when there were only 1 or 2 organized farming parties a week, because all regular people didnt go there anymore, with quadruple-clienting and the few people joining randomly got flamed out for taking up a space or "worse" actively playing on the afk team prolonging the point farming.

You better check for people not actively playing and kick them out early, also put some heuristics to check for people doing stupid things like only running one direction into a wall from putting a book on their keyboard or worse using bot programs (if unsure wait with kick but lower points immediately as that could be newbie players).

Also you could lower points by multiplying the fraction of activity/playtime of that match, both for people killing and people being killed. Checking activity at time of kill and factoring it in, like suggested above, seems a good thing to me as well.

Factoring in longtime success too much could be dangerous if people intentionally start putting their "champion" account to use as a dummy for farming.

Maybe you 'll have to think about why somebody would do that,

i mean, in the example wintertime gave, the game clearly was all about scoring points, and about participating/experiencing the game,

and if the creators set it up that way, it's gonna be played that way.

How do people know they 'r gonna be in team blue or red ?

can they choose this ?
can they make their own teams ?

this last one, making own teams, usually solves it for most games;

sure, people get teamed with crappy team-mates now and then, but after a while they 've made some friends,

and then, when an important game is about to played, they choose their friends to play with them in a team.

This is along the same lines as what Mippy suggested for global scoring system. I would suggest giving a personal goal as well as team goals that coincide, that way a player is gaining points for themselves and by happenstance they are winning for their team. That way if they are losing it is a personal loss. I would suggest objective based play over plain team death match as well since it keeps players focused. It also gives narrative to a needless conflict and problem solving lasts longer then blood lust.

You can't control players but you can keep them busy and reward them for following the learning curve as well as make it less fun when a player is changing the rules. However the best way to keep these players playing is to anticipate the common "rule changing" situation and design game play around those possible outcomes.

For example, if someone decides they are going to change the rules(friendly fire, voted off the team, etc), change that character's color from red or blue to purple. Enemy of all, friend to no one, yet. The team that kills the purple player has that player respawn as their color with no friendly fire for X amount of time. This keeps the player's head in the game but requires them to reorient their perspective of how they play. Since the game becomes complicated (purple) then regimented (respawn with team). Add objectives to this and a player should be kept in the game even after they decide to screw around for a bit.

Just a theory.