Kshatriya dharma has certain rules of engagement in battle.
Manu 7.90 - While fighting his enemies in battle, he shall hot strike with concealed weapons; nor with arrows that are poisoned, or barbed, or with flaming shafts.
Manu 7.91 - He shall not strike one who is standing on the ground, nor one who is a eunuch, nor the supplicant [one who has surrendered] with joined palms, nor one with loosened hair, nor one who is seated, nor one who says ‘I am yours;’
Gautama (10.18).—‘No sin is incurred in slaying foes in battle,—excepting those who have lost their horses, charioteers or arms, those who join their hands in supplication, those who flee with flying hair, those who sit. down with averted faces, those who have climbed in flight on eminences or trees, messengers, and those who declare themselves to be cows, or Brāhmaṇas.’
Baudhāyana (1.18.11).—‘He shall not light those in fear, intoxicated, insane or out of their minds; nor those who have lost their armour; nor with women, infants, aged men and Brāhmaṇas.’
Āpastamba (2.10, 11).—‘The Āryas forbid the killing of those who have laid down their arms, of those who beg for mercy with flying hair or joined palms, and of fugitives.’
Yajñavalkya (1.325).—‘He shall mot strike one who says I am yours, or who is terrified, or deprived of arms, or who is engaged with another person, or who has turned hack from the fight, or one who is only looking on the battle.’
Devala (Vīramitrodaya-Rājanīti., p. 407).—‘Who is eating straw, who is engaged with another, who is not actively engaged in fight, who is seeking shelter, the imbecile, one pressed by another, the religious student, the aged man, the outcast, the infant,—these shall not ho struck in lawful battle, by soldiers, even in times of distress.’
Manu 7.92 - Nor one who is sleeping, nor him who is without his armour, nor one who is naked, nor one deprived of his weapons, nor one who is only looking on and not fighting, nor one who is engaged in fighting with ahother person;
Manu 7.93 - Nor one who has fallen in difficulties regarding weapons; nor one in distress, nor one severely wounded, nor one who is frightened, nor one who has turned back;—the king remembering the duties of honourable men.
Do Kshatriyas have to abide by these rules when fighting enemies who do not abide by these rules?