Self defense being thrown out due to leaving the house is a bit of an over-simplification, but in essence, you can't claim you were in fear for your life when you were the aggressor in a conflict. There is a big difference in shooting somebody when they just broke down your door and going out into the yard and shooting somebody because they won't obey your commands.
no doubt...just like Zimmerman wouldn't have been able to hold to self-defense if he initiated aggression against Trayvon.