He/she could strike them broadly from behind, and the moment they turned around to retaliate... It was a slaughter.
The attacker failed to hit anyone from behind, and everyone got away unharmed. 
mnli hypothesis: The attacker failed to hit anyone from behind, and everyone got away unharmed.  premise: He/she could strike them broadly from behind, and the moment they turned around to retaliate... It was a slaughter.