Water and Oil
Sam's trick can be considered somewhat dirty. Particularly, when he saw the way these people carried themselves. They are too prideful and too focused on killing their enemies in one sweep.
If they really clashed, then one party will surely perish completely.
They wouldn't retreat, these people are close to barbarians. But he didn't care about feelings. Feelings don't win wars.
He also knew that the castle walls wouldn't stop them for too long, the more free time they have on them, the more beneficial it is for the enemies. The provisions are not enough at all the other party would gladly wait and plan on how to deal with the castle slowly, while the castle turned chaotic.
Sam didn't want that to happen. So, the first day went with him spraying hot rain on the enemies. It might not seem like much, but it is actually critical damage for the enemies. More than half of the enemies are completely soaked in the hot water.