A question from our study guide:

Third and 9 from A's 40. QB A2 takes the snap and scrambles. While A2 is in possession behind the neutral zone, B2 holds A3 at B's 49. A2 eventually quick kicks by punting deep. The punt rolls to R's 25 where it is eventually blown dead since no players are attempting to recover. RULING: If accepted, A will play a first and 10 at the 50.

True or False?

Is this a PSK foul or not? PSK doesn't give distinction for down or punt formation, it only says legal scrimmage kick other than made field goals and tries.

I would say PSK still applies. As you mentioned, the definition of PSK applies whether or not K lines up in scrimmage kick formation. I beleive the intent of the rule remains the same regardless of which formation K uses.

Lining up in scrimmage kick formation only adds extra protection to the snapper. So that rule is the only rule I know of that the officials would have to be careful not to call if K does not line up in a scrimmage kick formation.

I say it is false. Here's why.

Rule 2-23-4 says: A scrimmage kick is any legal kick from in or behind the neutral zone.

For PSK enforcement to take effect all three elements must be met: 1)The foul is by R beyond the expanded neutral zone; 2) the foul takes place during the interval between the snap and the end of the scrimmage kick that crosses the expanded neutral zone; and 3) the ball belongs to R when the down ends.

In your example you do not specifically state if the punt is from behind the expanded neutral zone, but I assume it is because no foul was called for an illegal kick. Therfore, the punt is a legal scrimmage kick from behind the expanded neutral zone, the holding foul occurs between the snap and the end of the kick that crosses the expanded neutral zone and the ball belongs to R when the down ends.
That is PSK enforcement by definition. It would be R's ball 1st and 10 at R's 15