When a unit closes with its enemies in close combat, character models will inevitably find themselves confronted by enemy troops. As described in the Close Combat section, models can attack any enemy models whose base they are touching.
Troopers confronted by character models will usually have the option of attacking a character or ordinary enemies, as bases will usually overlap slightly when models move into combat. Where a player has a choice of attacking characters or ordinary troops, he must nominate which model(s) be is striking against before rolling to hit.