The key thing about mumming is people dressing up, and in the prcess getting a bit of anonymnity which enables them to do things they otherwise might not get away with.

Such as on the one hand performing plays which might involve making rude remarks about impotant peopel; or going around negging, which can shade into demanding money with menaces.

But of course dressing up in disguise is also handy if you engaged in some kind of jacquerie - burning ricks or smashing machines. And sometimes very much the same kind of costumes have been used in this context too.

It'd be interesting to know how far these two traditions relate to each other.