Step 1: The Combat Showdown Step — Riftbound Rules

Section 459 — 18 rules

459.1.: Combat will open in one of two ways: when a Combat and Showdown are staged at the same Battlefield and the turn player initiates the Showdown; or when the turn is in a Showdown Open State and a Combat is staged at the Battlefield where the current Showdown is ongoing. See rule 318. Cleanups for more information.
459.2.: When Combat opens, it either opens with a Combat Showdown, or the current Showdown becomes a Combat Showdown.
459.2.a.: The following Tasks become Outstanding, in the order described:
459.2.b.: 1. Establish who is Attacker and who is Defender.
459.2.b.1.: The Attacker is the player whose unit(s) applied the Contested status to the Battlefield. They gain the Attacker designation now.
459.2.b.1.a.: This player gains Focus as the showdown begins.
459.2.b.2.: The Defender is the player who did not apply the Contested status to the Battlefield. They gain the Defender designation now.
459.2.b.3.: Units at the Contested Battlefield controlled by the Attacker gain the Attacker designation now.
459.2.b.3.a.: If a Unit controlled by the Attacker becomes present at this Battlefield after this moment, it will gain the Attacker designation during the Cleanup phase following the action that caused it to become present
459.2.b.4.: Units at the Contested Battlefield controlled by the Defender gain the Defender designation now.
459.2.b.4.a.: If a Unit controlled by the Defender becomes present at this Battlefield after this moment it will gain the Defender designation during the Cleanup phase following the action that caused it to become present
459.2.c.: 2. The Attacker gains Focus.
459.2.d.: 3. Add items to the Combat Chain if establishing Attacker and Defender has caused Triggered Abilities to become Pending.
459.2.d.1.: The Attacking player, who has Focus, places Triggered Abilities on the Chain first, followed by all non-Defender players in Turn Order, followed by the Defending Player.
459.2.e.: The State Closes if a Combat Chain was created.
459.2.e.1.: Otherwise the Combat Showdown continues, with the State Open as normal.
459.2.f.: Players proceed with any play on the Chain as normal.
459.2.g.: Focus does not pass upon closure of the Combat Chain, if any.