You can attack other players' halts - except night camps - by clicking on the halt camp on the world map. Select a hero with an army, then click on a halt to open the halt window. Next, click the "Attack halt" button and confirm by clicking the "OK" button. The battle calculator will then be displayed and load your last scouting report (if you have one). Finally, click the "Attack" button to trigger the battle. When a halt is attacked, the defender hero will either go back home if he loses the battle, or immediately leave camp to its destination (or its next halt) if he wins.