Imagine a kind of tower defence game where each player specialises either in defence or attack (a player is either one or the other in all games). In each game the attacker and the defender get separate scores. I want a leaderboard for the best defenders and a separate leaderboard for the best attackers. What are appropriate player rating systems in such a scenario? The ideal system is also efficient in that it produces robust rankings even if only a fraction of all possible attacker/defender combinations are actually played.
All the scoring systems I am aware of (e.g. Elo ratings or Microsoft TrueSkill) assume that both players are treated on an equal footing. I'd be extremely grateful for any pointers to relevant scoring systems.