This quest requires you to do melee damage to structures built by other players.

This isn't that hard if you pick your moment. Trying to knock down another players fort in the middle of a build battle might not have a very positive outcome.

Instead you will likely come across players structures from build battles that have finished and the surviving player has moved on. You will also find structures of players making their way across the map. This will give you some time to swing away and progress with this quest.