Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates as a saying of the Prophet (marfu'): "Whoever is killed in a blind melee, or by a stone, a whip or a stick, his blood money is the blood money of accidental killing; and whoever is killed deliberately, then it is retaliation; and whoever comes between him and it (the retaliation), upon him is the curse of Allah, His angels and all people; neither an obligatory nor a voluntary deed of his will be accepted."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنايات / 16044