def AB = new MagicStatic(MagicLayer.Ability) {
    @Override
    public void modAbilityFlags(
            final MagicPermanent source,
            final MagicPermanent permanent,
            final Set<MagicAbility> flags) {
        flags.remove(MagicAbility.Defender);
    }
}

[
    new MagicWhenBlocksTrigger() {
       @Override
       public MagicEvent executeTrigger(
               final MagicGame game,
               final MagicPermanent permanent,
               final MagicPermanent blocker) {
           return (permanent == blocker) ?
                new MagicEvent(
                    permanent,
                    this,
                    "SN loses defender."
                ):
                MagicEvent.NONE;
       }
       @Override
       public void executeEvent(final MagicGame game, final MagicEvent event) {
           game.doAction(new MagicAddStaticAction(event.getPermanent(), AB));
       }
   }
]