How do you make a Anti-Team killing script?

So recently I've been looking around for a Anti-Team killing script and none seem to work. Or if they do, they kill the person who killed you if they're on your team. I was wondering if anyone knows how to script a script that makes it so when you fire at your team-mate then he won't take damage, although the enemy will take damage. This is for my game 'Intensity' and it is a vital part for it.

Thank you for reading -iFluster

Add to sword a script:

--Touched function
--Check what player you hit.
--Check Team.
--If team, sword removes 0 health for 1 second.
--Function end

Sorry For not lua.