Rules patch: spears v8.3

This one is mostly a realism fix (for the narrative/roleplay-inclined out there), as spears themselves do not perturb the balance of the game in any way.

PROBLEM: although the "fight in extra rank" ability of spears nicely recreates the 'phalanx' combat technique, spears do not provide any additional benefit against charging cavalry (which was one particular usage in which the spear shined, particularly during the middle ages).

SOLUTION: a spear-wielding model on foot gains an additional benefit if it has not marched during its turn (it can however 'swift reform' and still gain this benefit). If such a unit is charged on its front by a unit of warbeasts, cavalry, monstrous cavalry or a monster, it gains +1 Strength during the first round of combat against those particular models only. Any attacks directed against enemy models that are not in contact with the front of the unit, or that did not charge this turn, do not receive this benefit. 

This provides good utility for spearmen units, especially when used defensively, making them more reliable against some of the worst hard-hitters in the Warhammer range, and the perfect answer to heavily armored cavalry. However, to gain this benefit requires them to severely sacrifice their mobility, and still does not increase significantly their ability to Wound their target in the first place, essentially preventing the rule from giving too much power for so few points (spears are normally 1 point/model).

With this rule, which is situational and rarely coming into play in an aggressive (forward-moving) army, the usage of spears in Warhammer becomes more realistic and coherent, and the dreaded 'schiltron' becomes a tool in a Warhammer general's arsenal.

EDIT: originally had the spearmen gain +1S instead of ASF. Although while logical, it ignored the fact that spears should strike the chargers first, regardless of the impact of the charge. But putting in both rules with no change in points would be overpowering, so I sticked with the ASF.
EDIT #2: the idea above was not really good... it rendered (quite obviously, if one wonders for a bit) Elven spearmen with no added bonus (as they already have ASF). So I went back to my original idea (a charge into spears grants extra force to the spear attack) and granted the next best thing to St bonus: +1 to Armor Penetration. 
EDIT #3: bonus from spears returned to +1S, as it originally was. This was inspired by the recent rumours about Warhammer Fantasy 9th Edition. Spearmen on foot are not overpowered as it is, and with the limitation of  not being able to claim this benefit if it marched, it is not an exaggerated benefit.