Red Guard initially abandoning sport (4)
I believe the answer is:
ruby
'red' is the definition.
(synonyms)
'guard initially abandoning sport' is the wordplay.
I cannot quite see how this works, but
'sport' could be 'ru' (rugby union) and 'ru' is found within the answer.
The remaining letters 'by' is a valid word which might be clued in a way I don't understand.
This may be the basis of clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for ruby that I've seen before include "Deep red - transparent gemstone" , "Jack perhaps" , "Precious red gem" , "killed an assassin" , "Gemstone - shade of red" .)