Art De La Guerre

[Ballista]

Two units, A and 1 in melee front edge to front edge.

A
1

Unit 2 wishes to slide down the side of A to give simple support.

1. Does it need to start corner to corner with A to do so? OR

2. is 1 able to slide down side of A from a position where it is not in corner/corner contact with A?

The rules appear to be contradictory here - P 41 seems to say Yes it can, definition of a charge P 42 seems to say no?

Obviously A and 1, 2 are on opposite sides.

[Ramses II]

P41 is the key page here. Unit 2 is contacting a new enemy that is already in melee (with unit 1), so it may slide along the flak to provide simple support (sliding along the enemy, 1st bullet). 

This is not a charge, so the unit does not have to stop on contact. 

[Hazelbark]

They are not contradicting. They are different situations.

On p 42 you are reacting to a unit that is charging an unengaged enemy.
On p41 you are seeing various examples of engage and unengaged and it explains when you can slide along the side.
A1 for example does not start corner to corner with B1
A3 is a case like that referenced in p 42

If the enemy is already in contact front edge to front edge before the unit in motion gets there, then the unit in motion may continue. If they enemy is not in contact, then the moving unit is the charger and will conform and not be permitted to more further.