Interception in endzone
 

The offense throws an interception in the endzone. The defense commits a holding penalty in the endzone after the interception and the intercepting team meanwhile returns the ball for a TD.

Whats the ruling?

Safety. 8-5-2c

If you look up the rule, you'll need to revise your use of the term 'offense'. In rule book terminology, the offense is the team in possession. 2-43-1

So it's better to state your case using A and B: B intercepts in the EZ and holds there, running it back for a TD. A will have the option to accept the penalty (safety, 2 points for A and B will free kick from their 20YL) or decline it (TD for B).

Even though A (offense) is responsible for putting the ball in the endzone, B's foul will result in a safety.

-The basic spot for B's foul is the 20 yard line (10-4-6)
-When the spot of the foul is behind the basic spot, the enforcement spot is the spot of the foul (All But 1; 10-6)
-A foul in the endzone by the team with the ball is a safety (FB Fundamental X-7)

Sorry Maven ... did not see your reply until after I posted.

It makes no difference where the INT occurs, the foul occurs in B's end zone. Therefore, it's a safety.

I thought he used the term correctly. He wrote that the intercepting team scored a TD after the defense fouled. Your answer seems to assume he screwed that up, because why would the foul by the defense in their opponent's end zone produce a safety?

Let's see if he clarifies.

The designations of A and B remain throughout the play. The designations of offense and defense change during the play based on who has possession. After the interception team B becomes the offense and team A becomes the defense. He continued to use defense to identify B after the interception.

Yep.

Peace

He wrote:
Why would he write what "the defense" does and then what "the intercepting team" does if he meant those to be the same team? I think he meant team A by "the defense" and team B by "the intercepting team". Why are you assuming the opposite?

After the INT, it's a simple running play. The basic spot is A's goal line.

CT1, hear is how I read the OP ... The offense (A) throws an interception in the endzone (B's EZ). The defense (B) commits a holding penalty in the endzone (B's EZ) after the interception and the intercepting team (B) meanwhile returns the ball for a TD.

Since A is responsible for putting the ball in the EZ, the basic spot is determined by 10-4-6.

10-4-6 . . . The basic spot is the 20-yard line for fouls by either team when the opponent of the team in possession at the time of the foul is responsible for forcing the ball across the goal line of the team in possession, and the related run ends in the end zone and is followed by a loose ball, regardless of where the loose ball becomes dead.

The following Case Book is similar.

10.4.6 SITUATION B: B1 intercepts A’s pass in B’s end zone, B2 clips A9 at B’s 10-yard line after the change of possession. B1 then fumbles in B’s end zone and the ball rolls out of the end zone and out of bounds at B’s 2-yard line. RULING: The penalty is enforced under the all-but-one principle. The basic spot is the 20-yard line. The penalty would be enforced half the distance, first and 10 for B on the 5-yard line. (10-4-6).

You would be correct if B fumbled in their own EZ following the INT. But that didn't happen in the OP.

Since B's foul occurred after the INT and there was no further COP, it's a simple running play.

Forgive the non-football guy, but I don't believe the part in red occurs in the OP. Thus, I don't believe this rule applies.

Because holding by A after an interception... especially behind the play, seems a near impossibility. I think it's a rather safe assumption that by "holding by the defense", he meant "holding by the intercepting team" or "holding by B"

Neither part of this clause applies: the EZ referred to is (in this play) B's EZ, and the OP ends in A's EZ.

And, as Altor points out, the play did not involve a fumble by B.

CT1 is correct: you have a running play by B that ends in A's EZ, where the result of the play is a TD for B. The basic spot would thus be A's GL, and since the foul was committed by the offense (B) behind the basic spot, ABO enforcement would make this a spot foul.

But you don't need to go through ABO reasoning here. I pointed out in post #2, 8-5-2c gives you the result of a safety directly.

Who knows why he wrote it that way?

I'm assuming the opposite because, as Mike notes, it's vastly more plausible, and a charitable interpretation demands that assumption.