I haven't actually learnt programming, so when I have to make a script I dig around the web a ton, but this time I can't find what I need anywhere :/

I want an npc to be passive before you enter a cell, but upon leaving he becomes aggressive. An example is the witch outside riverwood. I've checked the area out, but none of the markers or the red trigger box tell me anything. I also checked the witch herself, who didn't have any scripts on her. Any help would be appreciated, thanks