Can Cleave be used in response to opponent's spells, and does Cleave grant might increase when used while defending?

Ruling: Cleave cannot be used in response to opponent's spells, but can be used after the chain resolves. Cleave does not grant might increase when used while defending because it grants Assault, which only increases might when the unit is an attacker.

Nuances:

• Cleave can be used after an opponent's chain has fully resolved
• The Assault keyword from Cleave only provides might increase during attacking, not defending