Q: I am playing a team game and all the players in my team drop out of the game. Of course, I lose the game. Will I lose as many skill points as all the people who left me standing in the rain?
A: Unfortunately, yes. All alternative options are possible exploits for cheating:
If the TrueSkill ranking system does not count the game at all then the losing team can always ensure not to lose points by dropping out early (entirely).
If the TrueSkill ranking system only uses the team configurations at the end of the game then both the players that dropped would not be penalised and the remaining player can be arbitrarily boosted (that is, shortly before the end of the game all but one player drop from a team; for the update equation it would now seem that a single player has won against a team of, say, 4 players and would apply a massive positive update).
If the TrueSkill ranking system would introduce an arbitrary lowest rank in which every player falls that drops before the end of the game, then, again, the remaining player(s) in a team can be arbitrarily boosted (he won against the losing team and all the players that dropped. This approach would penalise the players that drop, though.
But: Players who drop regularly from a team would eventually be identified by the TrueSkill ranking system as having a negative impact on the team skill and will eventually be matched with other players of that have a negative team impact. So, you should not see this happening to often if you are a player of average skill.
Q: You are saying that the TrueSkill ranking system assumes that the skill of a team is the sum of the skills of its players. I think this model is not appropriate: I am usually playing much better with people from my friends list rather than with random players. Will this assumption lead to incorrect rankings?
A: The assumption that the team skill is the sum of the skills of its players is exactly that: an assumption. The TrueSkill ranking system will use the assumption to adopt the skill points of individual players such that the team outcome can be best predicted based on the additive assumptions of the skills. Provided that you and your friends also play team games with other players now and then, the TrueSkill ranking system will assign you a skill belief that is somewhere between the skill when you are playing with your friends and the skill when you are playing as an individual. So, in the worst case, every other game is not with your friends: then you are slightly ranked too high when you play with random team players and slightly ranked too low when you play with your friends. But, if you mostly play with your friends only the system will identify your skill correctly for most of your games.
Q: Does the TrueSkill ranking system reward individual players in a team game?
A: The only information the TrueSkill ranking system will process is:
Which team won?
Who were the members of the participating teams?
The TrueSkill ranking system takes neither the underlying exact scores (flag captures, kills, time etc.) for each team into account nor which particular team member performed how well. As a consequence, the only way players can influence their skill updates is by promoting the probability that their team wins. Hence, "ball bitches", "hill whores", "flag fruits", "territory twits", and "bomb bastards" will hurt their individual TrueSkill ranks unless what they are doing helps their team. Obviously, it is difficult to update individual players' skills from team results only. To understand the difficulty and the solution consider the following analogy: Suppose you have four objects (players), each having an unknown weight (skill). Suppose further that you have a balance scale (game) to measure weight (skill) but are always only allowed to put two objects on each side of the balance. If you always combine the same pair of objects, the only information you can get is which pair of objects is heavier. But if you recombine the players into different pairs you can find out about their individual skills. As a consequence, the TrueSkill ranking system will be able to find out about individual players' skills from team outcomes given that players not only play in one and the same team all the time but in varying team combinations.