Heavy chain carried by tennis player (8)
I believe the answer is:
henchman
'heavy' is the definition.
(thesaurus)
'chain carried by tennis player' is the wordplay.
'chain' becomes 'ch' (abbreviation for the unit of length).
'carried by' is an insertion indicator.
'tennis player' becomes 'henman' (I can't justify this - if you can you should give a lot more credence to this answer).
'ch' placed within 'henman' is 'HENCHMAN'.
Can you help me to learn more?
(Other definitions for henchman that I've seen before include "trusty supporter" , "Faithful helper" , "Collaborator, sidekick" , "Crony" , "Faithful supporter" .)