I think we can all acknowledge that this is confusing because it involves multiple rules.
@Calinative - you posted a rule from the San Diego County Football Officials Association, so just an FYI, I don't think that has the complete information, and it may not be up-to-date as the NCAA updates the rulebook each year. They even updated part of the targeted rules this year.
I download the NCAA rulebook each season, because I'm a nerd like that, so here's the link to the current 2026 version.
Cali is correct that we have to first look at Rule 2-27-14 (p.50 of the pdf above):
Defenseless Player
ARTICLE 14. A defenseless player is one who because of their physical position and focus of concentration is especially vulnerable to injury. When in question, a player is defenseless. Examples of defenseless players include but are not limited to:
i. A quarterback any time after a change of possession.
Change of possession is defined in the rules as including the moment a turnover (interception or fumble) occurs. (p. 37)
The term "defenseless" refers to the targeting, roughing the passer, or unnecessary roughness/late hit penalties. Rule 9-1 explains that "all fouls in this section...and any other acts of unnecessary roughness are personal fouls." (p.100) Unnecessary roughness does not have it's own section; the sections listed and described next are Targeting, Clipping, Blocking Below the Waist, Late Hit, Face Mask, Roughing the Passer, Chop Block, Leverage and Leaping, Contact Out of Play, Hurdling, Contact Against Snapper, Horsecollar, Roughing Kicker/Holder, Participation w/o Helmet, and Blind-Side Block.
The Appendix of the Rulebook has explanations and examples of the rules and how they work in practice. I usually find these very helpful. p.233 is the closest example to our situation here, although it's not exact.
Approved Ruling 9-1-4 (p.233)
A12 who normally plays quarterback is lined up as a wide receiver in the backfield and A33 is five yards behind the snapper in a shotgun formation. A33’s pass intended for A12 is intercepted. During the interception return B55 targets and launches at A33, striking him in the side of the helmet.
RULING: Foul by B55 for targeting and initiating contact at the head of a defenseless player. For purposes of Rule 2-27-14, A33 is a defenseless player since he played the down in the role of the quarterback.
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Conclusion: So yes, I realize that this is a targeting penalty, but if I am reading the entirety of Rule 9-1, I don't think we need to focus on that part. I can't find anything else that says that the QB wouldn't be a defenseless player, and given the way the rule is written, it seems like they made it so "unnecessary roughness" is basically a catch-all for when the player is defenseless but the offender didn't commit any of the long list of penalties above. I don't like it, and think it sucks, but unfortunately I think the ACC got this one right. Also, Cali is correct here.