Hamster Style scratching was originally used by the Hamster crew, where they reverse the cross-fader by taking it out of the mixer and turning it around. It can also be achieved by actually plugging the turntables in a reverse order to which you would normally expect. This allegedly makes scratching easier, and allows the DJ to work quicker, though it's not the way that I and others who spin music other than hip hop scratch.
Newer and more expensive dj mixers generally come with a hamster switch so no tearing apart equipment is required if you wish to both scratch and mix.