The same way you defend against most throws; grip fighting. In BJJ you know you shouldn't let someone with skill put a hand in your collar. The same goes for Judo, especially on your feet!
I am playing with it in bjj. I do it by droping to the knee. Not as explosive but less back exposure more control. However if you do this full speed and mash someone's ribs i don't think you need to worry about giving up the back.
You "could" stay standing, but you're better off going to the ground. Why? You can throw with more force when you throw your weight to the ground, plus you can easily get to kesa gatame for pin/control/sub and decide what to do next.