Islamic ruling on self-defence
Question

                What is the viewpoint of Islam toward self-defense?  Is it a right?  Are there conditions on that right?  Does the Quran speak to the issue of self-defense?
Praise be to Allah.
    Protecting oneself and one’s honour, mind, wealth and 
    religion is a well-established basic principle in Islam.
    These are the five essentials which are well known to Muslims. A 
    person has to defend himself; it is not permissible for him to consume that 
    which will harm him, and it is not permissible for him to allow anyone to 
    harm him. If a person or a vicious animal etc attacks him, he has to defend 
    himself, or his family or his property, and if he is killed he is counted as 
    a shaheed (martyr), and the killer will be in Hell.  

    If the harm that will result from this aggression is little 
    and he gives up defending himself for the sake of Allah, then undoubtedly 
    Allah will compensate him for that, so long as this does not cause any 
    increase in the wrongdoing against him or anyone else.