I have noticed Shaw plays a lot of break shots with the break ball favoring the back half of the rack, instead of the front half of the rack. I think (but not good enough to be certain), those are more likely to scratch.
Edit: he even seems to pick that as a break ball when he has one closer to the front half of the rack.
I wonder if it's the angle he's leaving. He seems to leave bigger angles on the break ball than the previous runners.