[kmunoz]

I would be disinclined to do something as straightforward as reducing Move to 1/4. You'd end up with some weird results, where for example a fat ogre with a Move of 4 will be just as slowed as a wingless pixie with a move of 4. In "reality" the pixie would be stopped in its tracks and the ogre would probably shrug most of it off.

So I think Ivalero's answer is probably the best, but if you want to model it through something more complex you could probably go with Binding (Area Effect; One-Shot; Sticky). This is technically a grapple, presumably a grapple with "two hands." Which means that with a Binding level of 4, the Break Free action requires a QC against 9 (4 + 5 for two hands). But with a Binding of 4 anyone with ST 10 or higher can still move, with encumbrance penalties. A character with ST 6 or less has a weight range of 40-240 lbs (p. B18), so on average about 140 lbs. So that's adding 140lbs of encumbrance, which reduces Move significantly.

All of the above is a terrible idea. Ivalero's answer seems best to me.