Expertise shown by service in court (5)
I believe the answer is:
craft
'expertise' is the definition.
(thesaurus)
'service in court' is the wordplay.
'service' becomes 'raf'.
'in' indicates putting letters inside.
'court' becomes 'ct'.
'raf' going inside 'ct' is 'CRAFT'.
'shown by' is the link.
(Other definitions for craft that I've seen before include "Vehicle for water or air" , "Vessel; skill" , "Occupation in which skill is needed" , "Art; ship" , "Cunning; boat, ship" .)