A character can join a skirmishing unit and fight with it, moving as a skirmisher while he does so.

Because the unit is spread out it does not benefit from the character's Leadership value. The unit makes all tests against the troops' own Leadership and the character is bound by the result.

Similarly, skirmishers cannot test on the general's Leadership if he is within 12', and cannot re-roll Break tests because there is a Battle Banner within 12"

In both of these cases the unit is judged to be so dispersed that the chances of all of its men seeing or hearing the commands of a character are nonexistent.