Easy way to earn this trophy is get the master assassin pack from Uplay in the rewards section. In it is a Templar lair mission where you can do a little side quest. Towards the beginning of it your targets will spot you and run away at the start of the chase after the first set of guards there will be two more guards blocking your path and one will have a broom in hand. Kill him quickly grab the broom and then whack the other guard before the mission desynchs from the target getting away.