Elvis, I think you're getting to why is this not a PSK foul?
In the statement of the penalty, under 9-1-16-a, any other personal foul against the kicker who is in the act of ot just after kicking the ball would qualify as a previous spot enforcement with an auto 1st down.
In full disclosure, I did not "invent" this down. It came from another source, although I doctored it a bit in my first post to clarify some things needed to allow us to more accurately determine the ruling. Now, I admit that I deliberately edited the question to assure that it had all the elements of one type of penalty enforcement (as you have noted), knowing fully well that such enforcement would be incorrect. So let's dive into it a bit.
The first thing we have to do is make a ruling regarding a possible Roughing (RRK)/Running Into (RNK) the Kicker foul. A17 moved outside of the tackle box (a fact that could have/should have been made more clear) before he kicked the ball. By doing so, he lost his 9-1-16 Roughing/Running Into the Kicker protection. So, there is no foul for Roughing/Running Into the Kicker.
However, B55's contact on A17 is described well enough that we can rule a 9-1-4 Targeting foul. So what's the penalty and where is it enforced?
Once we recognize that this is not RRK/RNK, then the foul is classified as (9-1-4) Targeting (TGT), only. The tendency by many, at this point, is to follow the penalty statement associated with TGT, which says that TGT is "15 yards," and makes no mention of the enforcement spot (for live-ball fouls). 10-2-1-a tells us that, when no enforcement spot is specified, the enforcement is by the 3&1 principle from the Basic Spot. 10-2-2-d-4 tells us that the Basic Spot for fouls that occur during the kick play portion of a down is the previous spot,
UNLESS the foul is governed by post-scrimmage kick (PSK) rules. So, is this foul governed by PSK rules? I'll shorten this discussion a little bit by stating that ALL of the elements required for PSK do, in fact, exist. (See my reply to dammitbobby at 11:25pm last night.) So, again, the tendency is to think that this is PSK enforcement.
Unfortunately, you'd be wrong. And getting to the correct enforcement is a bit indirect. But, let me take you directly to it. Go back to the penalty statement for 9-1-16-a. That penalty statement says that the penalty for RRK/RFH
OR ANY OTHER PERSONAL FOUL AGAINST THE KICKER or HOLDER is 15-yards
from the previous spot, plus a first down.
So, there you go. 15 from the Previous Spot, and auto-first for Team A. (And, being a legal kick down, the play clock is set to 25-seconds, and the game clock will start on the snap.)
Hope this helps.