From the Comprehensive Rules (Commander 2017 (August 25, 2017))
- 811. Alternating Teams Variant
- 811.1. Alternating Teams games are played with two or more teams of equal size.
- 811.2. Any multiplayer options used are determined before play begins. The Alternating Teams variant uses the following default options.
- 811.2a The recommended range of influence is 2. See rule 801, “Limited Range of Influence Option.”
- 811.2b Exactly one of the attack left, attack right, and attack multiple players options must be used. See rule 803, “Attack Left and Attack Right Options,” and rule 802, “Attack Multiple Players Option.”
- 811.2c The deploy creatures option isn’t normally used in the Alternating Teams variant.
- 811.3. At the start of the game, players are seated so that no one is next to a teammate and each team is equally spaced out.
Example: In an Alternating Teams game with three teams, A, B, and C, the seating around the table at the start of the game is A1, B1, C1, A2, B2, C2, A3, B3, C3, and so on.
- 811.4. A player can’t attack opponents who aren’t seated next to him or her.
- 811.5. In the Alternating Teams variant, a team’s resources (cards in hand, mana, and so on) are not shared. Teammates can’t review each other’s hands unless they are sitting next to each other. Teammates may discuss strategies at any time. Teammates can’t manipulate each other’s cards or permanents.