At the start of the Prussian move the French are over 400 yards away.
The Prussian infantry advance to within 90 yards, pinning the French.
The Prussian cavalry charge home. The French will get to fire at the cavalry. They will receive fire from the Prussians. The French, with six bases giving them a +1 offsetting the -2 for being unprotected against attacking cavalry, have a overall -1 modifier and that gives them a 20% chance to disorder the Prussian cavalry. The Prussian infantry have a 0 modifier and a 25% chance to disorder the French.
If no one is disordered the French will have a combat factor of -4 plus 1 for mass, giving them -3 against the Prussian cavalry on +4. The Prussian need to do five casualties to rout the French.
Assuming no disorder the French factor is -3 and the Prussians +4.
62% French Rout
28% French Disorder, Prussian cavalry bounce
9% Negligible outcome, Prussian cavalry bounce
1% Prussian cavalry bounce disordered
This time the Prussian cavalry move first.
The French fail to form square (they had a 70% chance of succeeding).
The Prussian infantry advance to give fire support (being careful to position the French in their left fire zone, something I haven't quiet clearly done in the picture) and the factors are the same for Example 1.
The cavalry move first.
The French form square.
In go the Prussian infantry.
This time both sides have a 0 fire modifier so a 25% chance to disorder the other side. The French would pick the Prussian infantry as the target as that would be the modifying unit.
Assuming no disorder the French factor is -4 and the Prussians -1.
26% French Rout
29% French Disorder, Prussian cavalry bounce
31% Negligible outcome, Prussian cavalry bounce
9% Prussian infantry disordered, Prussian cavalry bounce
5% Prussian Infantry rout, Prussian cavalry bounce
Applying the new optional Combined Arms Attack rule in NB IV (11.13 page 92) gives the Prussians a 60% chance of joining the combat. The Prussian player can avoid this by launching his cavalry in react phase. If the French fail to form square then the outcome is as for Example 1 and 2. If they do form square then the Prussian cavalry will bounce. The factors are French at +8 and Prussian at -1. The worst die roll outcome is a tie and one casualty each. The following movement phase sees the Prussian infantry hit the French in square. To avoid this you would have to employ the optional Emergency Lines from Squares rule (11.9.2 page 89) which would give the French a 40% chance of forming line.
There is also the issue of allowing a unit to close to within less than 100 yards if it was not going into close combat. However they are bound to be lots of legitimate moves that would place units within this range and pin the enemy. Then it would become an issue of only being in combat contact that would pin.
The reality is that the Prussians have used two units to try and take out one French unit. At best they have a 62% chance of success. Meanwhile, what are the rest of the French forces doing?
This is the chart for the melee outcome percentage calculations: