Forum:Royal oppression question

well can royal oppression negate the special summon of a monster like stardust dragon assault mode when it hits the field since royal oppression text says 'pay 800 life points to negate the special summon of a monster' and or an effect that special summons a monster. so if u miss the timing to activate it on assault mode activate can u activate in a chain when the monster has hit the field and negate the special summon.