防御 and 防衛: overlapping defense and defending a title
Read castle preparation, players' defense, gate and moat repairs, and a third successful title defense while separating purpose from success.
防御 (ぼうぎょ): a castle and players' defense
「守備隊は城門を固め、敵の攻撃に備えて防御を強化しました。」 (“The garrison secured the castle gate and strengthened its defenses against enemy attack.”) Read the purpose of preparing the castle's defense. Preparation does not report that an enemy attack was actually stopped.
「選手たちは組織的な防御で相手の速い攻めを防ぎました。」 (“The players stopped their opponent's fast attack with coordinated defense.”) The players actually block the opponent's attack. Unlike the preparation example, the defensive action's result is reported here.
防衛 (ぼうえい): repairs and retaining a position
「城の防衛に備えて門と堀を修理した。」 (“We repaired the gate and moat in preparation for defending the castle.”) Repairing the gate and moat has the purpose of defending the castle. The repairs alone do not establish a victorious defense.
「王者は三度目の防衛に成功した。」 (“The champion successfully defended the title for the third time.”) The champion succeeds in a third title defense. Success is explicit, unlike the purposes stated in the preparation and repair examples.
Read overlap, target, and success together
The castle-defense scenes show overlapping meaning. They do not support a fixed division in which one word is only for castles and the other only for players.
Identify whether the target is a castle, an opponent's attack, or a title, then distinguish preparation from a reported block or success. A defense word alone does not establish victory.
Do gate and moat repairs for defense mean an enemy attack has already been stopped?
Show the answer and why
No. The repairs give a purpose. The players blocking an attack and the champion succeeding in a third title defense explicitly report results in separate examples.