Does a friend's act of hitting a young man and a girl who were intimately close at the university, after witnessing their scandalous behavior, fall under the purview of the Hadith: "Whoever among you sees an evil, let him change it with his hand; if he is unable, then with his tongue"?

Enjoining what is good and forbidding what is evil are among the great شعائر (rituals/symbols) of the religion, and they have levels: changing with the hand, then with the tongue, then with the heart. Forbidding evil with the hand is permissible unless it leads to a greater harm. The religious texts have stipulated the obligation of enjoining what is good and forbidding what is evil upon the entire Ummah, not exclusively upon the ruler. It is permissible for individuals to change evil with their hand, such as removing evils that do not involve fighting or rebellion against the ruler.