Is striking the face absolutely forbidden in Sharia, or are there exceptions where it is permitted, and how can one defend oneself if it is forbidden?

It is forbidden to strike the face in any way, whether for discipline, education, training, the execution of a hadd punishment, or ta'zeer, based on the Prophet’s (peace and blessings be upon him) saying: “If any of you strikes [another], let him avoid the face.”

Scholars have unanimously agreed on the prohibition of striking the face, but they differed regarding qisas (retribution) for a slap to the face: 1. The Hanafis, Malikis, Shafi'is, and Hanbalis held that there is no qisas for it; rather, ta'zeer (discretionary punishment) is sufficient, due to the impossibility of exact equivalence. 2. Conversely, some Malikis and Hanbalis, as well as Ibn Taymiyyah and Ibn al-Qayyim, held that qisas is permissible for a slap, because it is closer to equivalence and because there are narrations from the Companions to that effect, provided that it does not result in greater harm than the original offense. This is the more preponderant view.

Accordingly, if the face is wounded as a result of a slap, then there is a hukoomah (a compensation, arsh), and qisas for a slap to the face is permissible, unless it leads to greater harm, such as the loss of eyesight.