Jockey got extremely bored in Kentish Town (9)
I believe the answer is:
tonbridge
'kentish town' is the definition.
(market town in kent)
'jockey got extremely bored in' is the wordplay.
'jockey' indicates an anagram (I've seen this in other clues).
'extremely' means to remove the middle letters.
'got' with its middle removed is 'gt'.
'gt'+'bored'+'in'='gtboredin'
'gtboredin' with letters rearranged gives 'TONBRIDGE'.
(Other definitions for tonbridge that I've seen before include "Public school" , "Kentish Town" , "Town in Kent" .)