The Vikings were extremely fierce in battle and considered by those they attacked as blood thirsty barbarians. Some of this reputation came from the Viking code of ethics that allowed for blood feuds to be common place. And in fulfilling this code nothing was deemed out of bounds. There's even evidence of battles involving multiple men against another man. Maybe not fair by todays standards, but back then justice could be enforced by anyone wronged and if it affected others well then It did force you to do right more times than not and think of others before acting, because if you didn't you could face a serious punishment that would most likely result in your death.