Can I use an Action spell while attacking to prevent my opponent from playing an Action spell?

Ruling: Yes, as the attacker you get Focus first after the initial attack/defend abilities resolve, allowing you to open a chain with an Action spell before your opponent can respond.

Sequence:

• Attack is declared
• When I Attack and When I Defend abilities form the initial chain
• Initial chain resolves
• Attacker gets Focus first
• Attacker can play an Action spell to open a new chain
• Once a chain exists, opponent cannot play Action spells

Nuances:

• Action spells can only be used during showdowns when there is no chain
• Unit abilities (like Warwick's) count as something on the chain, preventing Action spells from being played
• This blocking effect applies to both players once any chain exists