I would say that if you're going to have each kill increase one teams score while decreasing the other teams then you should start the game out at some number other than zero. Maybe have it start at 25 or 50, and if one teams score gets to be 0 then they lose, or if one teams score reaches 50 or 100 (depending on the starting value) then they win. You could set it up so assists, multikills, and skill type kills (sniper headshot for example) are worth more points to the killing team just so it is possible to have differing scores. For example, two kills to start the game could cause the score to be 23-27 (if started score is 25-25) if they were done individually, or 23-30 if it is a double kill with sniper headshots (2 points for 2 kills, 2 points for the 2 headshots, and 1 point for the double kill).