Ultimate is non-contact, so who is responsible when players collide?

Under Rule 12, every player must try to avoid initiating contact, and there is no situation where initiating contact is justified. "Making a play for the disc" is not an excuse.

• A player in an established position is entitled to stay there and must not be contacted.
• You may take any unoccupied position, as long as you do not initiate contact or move recklessly. While the disc is in the air, you may not move just to block an opponent's path to it.
• Before you dive, leap or jump, you must be reasonably certain you will not initiate contact. If it is unclear who initiated contact and one player dived or jumped, that player is deemed to have initiated it.
• The player who initiates contact is the one who arrived after the opponent had established their position, or who changed direction so that contact with a legally moving opponent became unavoidable.
• Minor contact (minimal force, not altering anyone's movement) is not a foul. Contact with a player's arm or hand that is about to touch, or is touching, the disc is never treated as minor.
• Dangerous play (reckless disregard for safety) is treated as a foul whether or not contact happens.
• If two players moving to the same spot make non-minor contact at the same time, it is treated as offsetting fouls and the disc goes back to the last undisputed thrower.