Can Guerilla Warfare be used in a showdown as a reaction if it doesn't specify action or reaction?

Ruling: If a spell or ability does not have the keyword "action" or "reaction," it can only be played/used during your turn. It cannot be used in showdowns or to react to other spells/abilities/units unless it has the keyword reaction.

Nuances:

• The absence of action/reaction keywords means the card defaults to only being playable on your turn
• Reaction keyword is specifically required to use cards in showdowns or in response to opponent actions