Rule 464.2.c.3

The attacker and defender gain the Attacker or Defender designation now, as appropriate. Units at the Contested Battlefield controlled by the Attacker or Defender gain the Attacker or Defender designation now, as appropriate.

• 464.2.c.3.a If a Unit controlled by the Attacker or Defender becomes present at this Battlefield after this moment, it will gain…

Official Core Rules