can a son retaliate if his father attacks / hits him without any valid reason / excuse,

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

We have previously clarified the high status of parents and their great right on their child, so please refer to Fataawa 84942 and 87019.

If it happens that the father transgressed his child by beating him or so, it is impermissible for the child to deal with his father in the same manner, such as to strike him back, as it is impermissible for a child to beat his father. For more details, please refer to Fatwa 92093.

Hence, if both or one of the parents treat their child badly, it is impermissible for the child to respond to that in the same way they treat him, otherwise, he will be an undutiful child. For further information about the great risk of undutifulness to one’s parents, please refer to Fataawa 85041 and 87856.

Allaah Knows best.