Indifferent, lethargic, inert, apathetic.
Don’t be lethargic when (lit. even if) someone is going to attack you.
That person is just apathetic even if someone boxes him.
To neglect s.o., to fail to give s.t. proper attention, to leave s.o. to or by himself.
She leaves the child to himself no matter where he goes.
That doctor does not neglect his patients.
The child fell because she failed to give him proper attention.