Relishes holding in a bit of smart, pert talk (9)
I believe the answer is:
sauciness
'pert talk' is the definition.
'relishes holding in a bit of smart' is the wordplay.
'relishes' becomes 'sauces' (I've seen this before**).
'holding' indicates putting letters inside.
'a bit of' indicates taking the first letters.
The initial letter of 'smart' is 's'.
'sauces' enclosing 'in' is 'saucines'.
'saucines'+'s'='SAUCINESS'
(Other definitions for sauciness that I've seen before include "Disrespect" , "Causes sin in jaunty or impudent state" , "Impertinence, cheekiness" , "Causes sin through kind of impudence" , "Brass" .)