Movement, in the system, is never by stack is it? it's always by unit.
Opportunity Fire, in the system, is always directed at "the moving unit" as it happens in response to movement
What a Cavalry charge does is focus that "movement" into a specific location--target...as a unit moves OF can address it....
So---I would see the 1st cav charging---disrupted, he stops....1 OF....2nd cav charges....if he disrupts...he stops...Op fire done....
if there is a 3rd cav...that's a problem for the inf.....(can a cav unit charge through a disrupted friendly unit ?? if it was napoleonics....no......
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OR if no disruption occurred then there is no 2nd OP Fire as it's now assault---
So if the 1st cav made it in past the OP fire---it would wait to resolve until the other units finished their Assault move/overrun....
I don't think you ever get to take 2x Opp fire on a stack of 3 units moving....that's mixing different mechanics in an invalid way I think....
The Op fire thing that I just figured out is those 82mm mortars.....they can opp fire x2, and if they can see the target...it's pretty good stuff...
cj