Slitherine

In dementia land a unit of desperate unit of persian foot was charged by some cavalry, nearby a unit of immortals passed the cmt and did a intercept charge so as the cavalry would hit both units. The question being do the immortals get to shoot with the rear rank as they moved in the intercept phase.

No, the intercept would count as a charge.

Rob

Normally the intercept only counts as a charge if it is a flank or rear interecept. In a frontal intercept, the interceptor moves into the path of the charge and then the charger charges into the interceptor making the interceptor a target of the charge.

I understand your reasoning but I am not sure the RAW (don't have the rules in front of me) implicitly forbids support shooting in this instance. Maybe an author could clarify.

I think this is analagous to foot intercepting shock mounted, where the foot are treated as charging even though they are stationary at the point of impact.

No, the word "charge" in "interception charge" means they are charging, it's just that in this case the enemy charge is not cancelled.

The Immortals don't get to support shoot because such archer "must be supporting medium or heavy foot of the same stationary battle group" - and the battle group is not stationary. Also, If the cavalry are shock troops, the won't get a + POA for light spear either

It is still an interception charge. Not strictly an answer to the OP, but from the FAQ

Do interceptors use the POAs for their troop type as if charging?
Yes. These factors are designed to represent their physical momentum of movement forward. So lancers intercepting
have the benefit of this. Certain foot intercepting mounted will find this difficult and lose POAs they would have if they
were instead receiving a mounted charge stationary.

Like I said, I didn't have the rules in front of me.