Restriction

For Restricted cards, see Banned and restricted cards.

Within the rules of Magic: The Gathering, a restriction is an effect that precludes one or more creatures to attack or block.

From the glossary of the Comprehensive Rules (June 7, 2024—Modern Horizons 3)

Restriction

An effect that precludes one or more creatures from attacking or blocking. See rules 508.1c and 509.1b.

From the Comprehensive Rules (June 7, 2024—Modern Horizons 3)

• 508.1c The active player checks each creature they control to see whether it’s affected by any restrictions (effects that say a creature can’t attack, or that it can’t attack unless some condition is met). If any restrictions are being disobeyed, the declaration of attackers is illegal.

  Example: A player controls two creatures, each with a restriction that states “[This creature] can’t attack alone.” It’s legal to declare both as attackers.

From the Comprehensive Rules (June 7, 2024—Modern Horizons 3)

• 509.1b The defending player checks each creature they control to see whether it’s affected by any restrictions (effects that say a creature can’t block, or that it can’t block unless some condition is met). If any restrictions are being disobeyed, the declaration of blockers is illegal.
  A restriction may be created by an evasion ability (a static ability an attacking creature has that restricts what can block it). If an attacking creature gains or loses an evasion ability after a legal block has been declared, it doesn’t affect that block. Different evasion abilities are cumulative.

  Example: An attacking creature with flying and shadow can’t be blocked by a creature with flying but without shadow.