Sure, you can fight back, unless of course there are 3 of them with guns, and you only have one.
This is a totally separate issue -- what do you do when you are outgunned and/or outnumbered?
The answer of course is you run and then you take cover.
It's a separate issue of the same thing.
The USA has the HIGHEST murder rate in the first world. By a large margin too, it's not even close. The US is also the only country in the first world which has such lax gun laws. Switzerland has lots of guns, but not lax gun laws, but even then its gun murders are higher than the UK's gun murders, even though it has a lower murder rate.