Clan Skab

Regarded as some of the finest warriors in Skaven society, Clan Skab 's Clanrats are often leased out to other Clans for service. Even more important, Clan Skab tends to produce more Black Skaven than other Clans, and so they have an inordinately high number of Stormvermin in their ranks. These expertly trained warriors are often sold to other Clans to act as guards for Chieftains and Warlords, or are claimed by the Grey Seers for similar purposes.

Source

 * Warhammer Fantasy RPG 2nd ED -- Children of the Horned Rat (pg. 50).