The word "retainer" used in
rap vernacular often is referring to keeping a thug on hand that is willing to do dirt. The celebrity retains this person's services thru cash payment, or other bartering options such as weed or
pussy in the event that a punch needs to be thrown (or otherwise) and the celebrity would be open to a potential costly lawsuit, whereas the retainer does not have enough
money worth be sued for, etc.
When Charlemagne
Tha God was instigating
Nelly during an interview, he was warned "Hey,man...just say what you wanna
say. We're all men. I keep retainers just for guys like you".