Stopping cavalry charges

[Didz]

But isn't evasion usually done to the sides, rather than dead ahead ?

Nope! not on wargame tables anyway.

Quote from Charge or How to Play Wargames by Peter Lawford, Chapter 6 Charges and Melees (page 67). The Charge Rule 4.

It may happen that a charge has been ordered from too far away for the defending troops to be 'pinned', and that these troops have orders to move. If a projected move, when completed, takes these troops beyond the maximum movement distance of the attackers, the move must be carried out, and there will be no melee. If on the other hand, after the move has been carried out the attackers can still reach their prey, the defenders carry out half of their move only, and then must stand and fight.

Quote from Rules for the American Civil War 1863 published by the British Model Soldier Society. Section 11. Move Penalties Rule A.

Cavalry and Infantry may charge provided that the movement is intended to bring them into contact with enemy troops during the bound in which they charge. If it becomes obvious that contact is not going to be made, a normal move must be taken.

The wargames Research Group Rules for 1750-1850 provide a slightly different slant to this rule in that they force infantry being charged from more than half a charge move distance away to either form square, or retreat into cover. This overides any other orders the infantry may have had prior to the cavalry threat being spotted and is intended to reflect the standard practice of the period. Infantry caught in the open by cavalry and unable to form square because the cavalry are within half their charge move distance are more or less certain to be routed and the charge becomes a pursuit. The only way the infantry could avoid this fate is if they inflicted at least 20% casualties on the charging cavalry effectively forcing them to baulk and abort their charge.