If the creature is neither an attacking creature nor a blocking creature at the time the spell resolves, it will have no effect.
Choose target creature. If it's attacking, it can't be blocked this turn. If it's blocking, prevent all combat damage that would be dealt this combat by it and each creature it's blocking.
This spell can target any creature. The check for whether that creature is attacking or blocking made on resolution, and it will have the appropriate effect at that time.
