It often happens that two or more units are lined up next to one another, so that a charge against one will result in others becoming involved (see Fig.1 below).
In Figure 1, for example, a charge against the left hand unit will inevitably bring the other unit into combat. In a case like this the charging player should declare his charge against whichever unit he intends to bring most models to bear against. However, because it is inevitable that other units will be brought into the combat they are also allowed to make a normal charge response – ie, a unit can flee, stand & shoot or hold even if it is not the target of the charge, if it is inevitable it will become engaged in the combat.
Of course, units will normally not line up exactly. It is inevitable that a charge will reach one unit before the other if only by a fraction of an inch. So, where do you draw the line? If a unit is a fraction of an inch behind one to its side, does it avoid combat or is it drawn into the fighting?
The best way to deal with this is to stop the charge as soon as it hits any unit then align the charge to the unit as normal. If the process of alignment carries you into further enemy units then those units become drawn into the combat and the whole lot are aligned into a battleline in order to bring as many models into combat as possible. In these cases it is often necessary to move all the units, chargers and targets, in order to form a convincing battleline. Units hit during realignment have the usual options for charged troops: they can flee, hold or stand & shoot.
It can happen that a unit finds itself just out of combat because it is fractionally further away than one lined next to it, or at a slight angle compared to the chargers. In reality the chargers would not simply stop and form a neat line whilst their enemy are so close. Therefore, the chargers are automatically moved into contact if they are within 1" of the second enemy unit and assuming the chargers have enough move left to reach them. Move the enemy unit into position, as this is usually easiest, or shuffle all the units together until a battleline is formed.