enforcement question

[dammitbobby]

This is a question from a quiz (reputable source) and I don't understand how they got to their answer. 

1/10 @ A-20. A99 catches a forward pass at the 50 and runs to the B-28 where he fumbles. B97 picks up the ball and runs to the B-49 where he fumbles. A86 jumps on the ball at the 50. B77 is flagged for roughing the passer.

They listed the answer as 1/10 @50. My answer was 1/10 @A-35.

My reasoning:
10-1-2-2-c-3: When the team not in possession commits a foul either behind or beyond the basic spot, the penalty is enforced at the basic spot. (the foul occurred behind the basic spot)

so what's the basic spot?
10-1-2-3: Pass Plays: Previous spot, on legal forward pass plays.

Previous spot is A-20, so I have this as 1/10 @A-35.

What am I missing, or is the answer on the quiz wrong?

[sj]

If the penalty would be accepted it would be A 1/10 @ A35. So they'll decline it and take the ball w/ A 1/10 @ 50.

[dammitbobby]

So why the 50 though, that's there the pass was completed? Or the 50, because it says that's where A86 recovered the ball? That can't be right, so must be former.

Based on your response, I'm guessing the explanation has something to do with play segments?

[sj]

It could be put this way. They'll decline the penalty and take the result of the play w/ A 1/10 @ 50 since that's obviously a better outcome.

[dammitbobby]

AHHHHHHH I got it now. 

*A* recovered, not B... My brain read the play as B recovered and I couldn't figure out how A was getting the ball at the spot where B recovered. Makes total sense now, thank you!

[sj]

The good thing is, that fact wouldn't have escaped you on the field.

[ElvisLives]

And we should always consider clock status in these questions.
Play clock duration?
Game clock starts…?

[dammitbobby]

PC 25, GC on R's signal.

[ElvisLives]

PC 25, GC on R's signal.

 

Now explain why, in both cases.

[dammitbobby]

On the ready  for 2 reasons:
3-3-2-e: For each of the following reasons, the game clock is stopped on an official’s signal. If the next play begins with a snap, the game clock will start on the referee’s signal:
3-3-2-e-1: Team A is awarded a first down, either through play or by penalty
3-3-2-e-4: To complete a penalty

Play clock 25 reason:
3-2-4-c-1: If the officials signal the game clock to be stopped for any of the following reasons, the referee shall signal (one open palm in an over-the-head pumping motion) that the clock should be set at 25 seconds:
1.Penalty administration.

Appreciate you challenging me to get more in the rules and understand the why.

[ElvisLives]

Expounding a bit, some folks may (erroneously) think that the game clock would start on the snap because of the change of team possession during the down. Incorrect. The ‘change of team possession’ thing only applies if Team B will next snap the ball. In this case, they will NOT next snap the ball, and there is no other reason that would cause the game clock to start o the snap, so the game clock starts on the referee’s signal.