Akira didn't expect the punch so he was hit full on. But he quickly got his footing back again and returned the blow without hesitation. Good for Akira was that the police was not allowed to just kill black cats, otherwise they would have long since been wiped of the face of earth. Murdoc shouldn't have seen Akira coming out of the apartment because his back had been facing it. Akira was ready to fight the threat in front of him. The normally quite naive and childish looking Akira now actually seemed quite fierce. Contrary to those thugs from before, Murdoc probably has never fought a street cat before.