The ball’s failure has its own procedure
Law 2 provides a retake when the ball becomes defective while moving forward from a penalty before touching a player or the goal frame. This is different from a normal shot simply missing or being saved.
Imagine a penalty whose ball visibly loses its shape before reaching the goalkeeper. The goalkeeper’s later contact does not explain the whole incident if the defect already arose earlier. The timing of the failure determines which sequence the law describes.
Follow the shape from the kick
A camera showing only the keeper’s save may conceal when the problem began. The more useful replay follows the ball continuously from the foot. Distinguish a ball that became defective from a merely unusual spin or flight; a strange-looking shot alone is not proof of a faulty ball.
The retake does not add an extra attempt to a scored first penalty. It replaces an attempt affected by the specified defect. This explains why the official can arrange another kick even without a visible encroachment offence. Other ball failures have their own restart treatment, so the example is deliberately confined to the forward penalty flight before the first player or frame contact.
Questions answered
Does an odd flight alone establish a defective ball?
No. The defect itself must be established.
What matters in the replay?
When the defect arose relative to the first player or frame contact.
Sources & further reading
Official references for the subjects discussed. Service terms and device software can change.