If Ezreal moves in as an attacker, kills the only defender with his effect, then the opponent uses Ride the Wind to bring in a new defender with lower might than Ezreal, who gets pushed back?

Ruling: Ezreal gets pushed back. He is the attacker.

Nuances:

• Even though Ezreal has higher might than the new defender, the attacker is always the one who gets pushed back when a new defender enters after the original defender is removed