As the cutter (red2) starts to cut open-under, if the defender (blue2) remains in-line, they will find themselves on the back foot, with red2 able to choose to beat them inside or outside. If instead blue2 decisively takes an inside or outside line, they can force red2 off their ideal cut.
Looking at inside first - as red2 steps towards the open side, blue2 immediately steps to take the inside line
As the cut progresses, blue2 uses their position to push red2 outside, always holding the inside line
This forces red2 off their straight-line cut and away from the handler; disrupting timing and spacing
Alternatively blue2 could choose to do the opposite
This time blue2 immediately steps to the outside
As the cut progresses, blue2 forces red2 into a narrow cut, towards the handler
Again resulting in a poorer cut