Girl jockey, car thief
I believe the answer is:
joyrider
'car thief' is the definition.
(I've seen this before)
'girl jockey' is the wordplay.
'girl' becomes 'joy'.
'jockey' becomes 'rider' (I've seen this before**).
'joy'+'rider'='JOYRIDER'
(Other definitions for joyrider that I've seen before include "Criminal driver" , "Driver of stolen vehicle" , "He drives stolen cars for fun - sounds ecstatic" , "(Temporary) car thief" , "One driving a stolen car" .)