[MJT]

This is a rule that a few of us, myself included got changed. Bob M and SRH were the instigators and asked a few of us to get involved.

Here it is a little simpler.
Let's say A is running for a TD, but fumbles the ball into the EZ and B65 picks it up and while in the EZ A22 grabs and twists the face mask of B65. B65 fumbles the ball while in the EZ and it goes out of the EZ, goes OOB's at the 3, or is recovered by A78 at the 3. In this case the 15 yard penalty will be enforced from the 20 yard line, making it 1-10 at the 35.
Why; team A was responsible for forcing the ball across the goal line of B, and fouled B while B was in possession and B then fumbled the ball in the EZ. It doesn't matter where the ball becomes dead, enforce the penalty from the 20.

Now let's look at the other possibility.
Let's say it is 2-10 at A's 2 yard line and A35 gets a handoff and floats back into his EZ and B90 grabs and twists the face mask. A35 fumbles the ball while in the EZ and it goes out of the EZ, goes OOB's at the 3, or is recovered by B45 at the 3. In this case the 15 yard penalty will be enforced from the goal line, making it 1-10 at A's 15.
Why; team A was responsible for forcing the ball across their own goal line, and was fouled by B and then fumbled the ball in the EZ. It doesn't matter where the ball becomes dead, enforce the penalty from A's goal line.

Now, the foul need not be in the EZ, but the run must end in the EZ.
The keys are
1. Who is responsible for forcing the ball across the EZ?
2. A foul occurred by the opponent of the team in possession.
3. The run ended in the EZ, (fumble).

Hope that helps. I don't have my new books yet to see what, if any case plays were added.