To choke, losing heart in Wimbledon, is hard to explain (7)
I believe the answer is:
strange
'hard to explain' is the definition.
(I've seen this in another clue)
'to choke losing heart in wimbledon' is the wordplay.
'to choke' becomes 'silt' (silting is a kind of choking).
'losing heart' suggests removing the centre.
'in wimbledon' becomes 'range' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'silt' with its middle removed is 'st'.
'st'+'range'='STRANGE'
'is' acts as a link.
Can you help me to learn more?
(Other definitions for strange that I've seen before include "Odd, peculiar" , "Unusual, odd" , "Slightly odd, a bit weird" , "Weird, eerie" , "Eccentric" .)