Small forwards are typically not as good of shooters as a shooting guard (hence the names). Shooting guards shoot. Small forwards are typically just that: forwards who are too small to be a power forward. They don't typically have the shooting prowess and ball handling skills of a guard (sometimes more streaky as shooters), but aren't powerful enough to play down low consistently (though most can do that for stretches). This is why they are also commonly referred to as "swingmen".
Marble is really a tweener at any of his positions. He's not a guy that will hang down low, at least not right now. But he also isn't a great shooter. He's got good handles, though.
I think he's got the ability to possibly be a 2 when he's a senior. But right now, he doesn't quite fit in that mold. But then again, he doesn't really fit ANY mold at the moment.