Why do people call her Leaf?

Well, for whatever reason they call her Leaf, I don't think it's that bad of a name... it can give you nice ideas. I once tried to picture her character in my mind, imagining her story and stuff like that. I came up with Leaf being a shortened version of her nickname "Razor Leaf" (which is a pretty badass one) and her real name being unknown. Er... was that odd? Her name inspired me. Yeah, I know, I'm weird. Just ignore me.

Ya know, That kinda makes sense. Who wouldnt want a badass name like Razor Leaf.. Right?

I would say that Leaf is because of LeafGreen, to avoid confusion on the fact of Blue Oak/Ookido Green. Simple as that...

Also, on a semi-related note, Blue is not Terry probably because of GSC (consequently HGSS) canon having solidified a name for this rival for several years now.

Game name-wise, I always called her Leaf or Green and the rival as Blue (though I mostly refer to him as Gary, lawl). I don't see what's wrong with calling her Leaf, it doesn't seem al lthat awkward to me.