The red zone above depicts an area on the table that will cause you to scratch if pocketing the object ball in the other corner using a stun shot. A sample shot is shown where the object ball is pocketed in the bottom corner and the cue ball scratches in the top corner.
To avoid a scratch, use follow or draw to bend the cue ball path off of the tangent line. The further away the cue ball is from the pocket, the easier it will be to avoid a scratch.
If you have a shot where the object ball is near the red zone, be careful!