As with combat between ordinary warriors, casualties inflicted by a character can extend beyond the models the character is touching. If a character has say, 4 Attacks and is facing two enemy troopers then his attacks are worked out against these. However, if the character scores sufficient wounds to slay three or four models then the enemy unit loses three or four troopers, not just two.
Don't be fooled by the fact that models are static and the battle lines rigid and straight. What is represented is real combat! Heroes are just the type to strike boldly left and right, stepping forward to deliver fresh attacks, cutting down foes who step forward to fill a gap.
If a character attacks an enemy character, or another individual model such as a monster, then any excess wounds caused by those attacks are not carried over onto ordinary troopers fighting alongside. The attacker has chosen to concentrate his attacks on a single special foe and any wounds left over are wasted and do not count cowards the result of the combat. The exception to this rule is during the challenge as described next.