I believe the guide above is wrong. This achievement should relate to a Stronghold match, and you will need to be on defense. The rounds alternate, so you'll get a lot of chances. If you're boosting this achievement, just have the attacking team stand still until the time runs out - about three minutes depending on the map you're playing. if you're in a public game, you'll eventually get this one... I've played a lot of stronghold and it's not at all uncommon for the attackers to fail the first objective, usually in Blackwater or Escalera.