[mbyron]

Note that even with a loss of down, an illegal forward pass can result in a first down due to the run preceding the foul.

For example: 3rd and 2 on A38. A1 drops back to pass and then runs up to the A46, where he throws a forward pass to A2.

This is an IFP thrown beyond the neutral zone. The 5 yard penalty is assessed from the end of the run, which will put the ball at the A41. Since that's beyond the line to gain, the loss of down is ignored, and it's 1/10 for A at the A41.

At first, this provision of the rule struck me as odd. Why should A benefit from an IFP? The answer is that they don't benefit from the IFP (which incurs a penalty), but the run is not taken away from them. A gets the benefit of the run up to the point of the foul. If that run, less the penalty, is still sufficient for a first down, then good for A.

Of course, one might ask why this isn't a loose ball play and thus enforced from the previous spot. The answer is: an illegal forward pass does not fall under the definition of a loose ball play.