Getting punched in the nose gives you the right to shoot the person.

[Lizzie Poppet]

17. In the vast majority of jurisdictions...

In the vast majority of US jurisdictions and in most such situations, a person is permitted to use lethal force when they are physically attacked. There are some exceptions, such as when the "attacker" clearly represents no significant, substantive threat to the person attacked, but those situations are unusual.

The Zimmerman defense seems to be making this a key aspect of their argument, and apparently Florida law backs them up.

I have a huge problem with this, of course. Not with the basic idea that using deadly force in response to physical assault can be permitted, but with applying that principle to someone who initiated the confrontation and whose behavior made the other party fearful for their safety. Zimmerman's actions precipitated the entire encounter, and that places responsibility for the outcome on his shoulders, IMO.