Don't know what happened exactly in this instance, but if something like this were to happen in my game, I think I would lean toward calling this simultaneous if at all possible. (Or, be unable to discern which one came first. ;) ) However, if these fouls CLEARLY happened one, then the other ... then it is what it is.

I understand this is the way the book tells us to administer these fouls. However, I've never liked it. On dead ball fouls that occur after a first down was gained, the chains should not move with the foul.

Think of it logically.

3rd and 10 from the A-20, they gain 15. At that moment, they've gained a first down, from the 35. Then they earn a dead ball 15-yarder. It SHOULD BE (not by rule, I know...) 1st and 25 from the 20. There is a logical inconsistency in giving the 1st down when they earned it, but then not resetting the chains until after the DBF.

Consider the same thing, but the 15-yarder occurs after we've set the chains. NOW it's 1st and 25. Why should the application of the penalty depend on how quickly 1 official signals the RFP or 3 non-players happen to move their equipment? Either the foul occurred DURING the down, or AFTER the down... we're treating it halfway one way and halfway the other. Dumb.

Yes, that's the way to do it if you can. In this case, I couldn't fake it. :)

Going back to the not resetting the chains after a dead ball foul before the RFP would go a long way - good point.

Short answer to the highlighted question: because that's when the new series begins.

Longer answer: we have 3 real-world time intervals (not clock-time) to consider:

1. The time before a series ends (for instance, by reaching or failing to reach the LTG).
2. The time after a series ends and the new series begins.
3. The time after a new series begins.

In the context of your question, there are no dead ball fouls during (1), because the ball is live.

So dead ball fouls occur during (2) and (3), and they are penalized accordingly.

You might not like how it works, but it's certainly logically consistent.

Put that way, I guess my point is that item number 2 should not exist. The new series should begin the instant the old one ends.

That's the way it used to be. The rulesmakers felt that 1st-and-25 was basically a turnover, and too severe for a "heat of the moment" foul just after the play ended.

Another reason why an all-but-one should never be marked off from behind the line of scrimmage (the NCAA rule is good here, IMO), but that's an argument for another thread.