If someone performs homosexual acts or tries to do so on somebody, then can one fight with him or beat him, I mean to say can one indulge in a fight with him?
Anyone may defend himself or herself if a violation of their personal space occurs.
Any unwelcome contact may be rejected or protected against. This includes but is not limited to physical force if it becomes necessary. Violence, though discouraged in Islam, could be exercised as a last resort if the situation calls for it. One should always make a wise decision as to their reaction and be judicious in any circumstances. Although the permission of violence avails a person to protect themselves a person should be real careful to judge the situation and not overreact. If a person makes a pass at you by simply asking you out or suggesting something you do not like you should not react by punching the person; that is not what the allowance is for.
Finally, an individual – as opposed to the state – does not have the right to punish another person for any wrongful acts.
I hope I have clarified the issue.
God knows best.