A zig zag scratch is a move where the DJ uses one hand on the record, and one hand moving back and forth between the volume fader and the record to create a unique zig zag scratch effect. If scratching, zig zag scratch, with your right hand on the record the technique would go something like this:
right hand pulls back sound and lets go
left hand taps the record as it's coming back forward to make a quick pause in the forward movement of the sound to make two distinct forward sounds instead of one.
left hand quickly moves and taps down the volume fader a small increment to make the volume a little lower (or higher since you could do the same thing in reverse).
repeat pattern. zig zag scratch.
The effect you get is a 1,2,3 1,2,3 1,2,3... scratch of the sound while the 1,2,3 fades out a little more each time the volume fader is tapped a little lower (the sound can be faded completely out or you can start fading the sound in and out). zig zag scratch.