Victor loses his head in the bull ring (5)
I believe the answer is:
inner
'bull ring' is the definition.
'inner' can be an answer for 'ring' (I've seen this before). I'm not certain of the 'bull' bit.
'victor loses his head' is the wordplay.
'victor' becomes 'winner' (synonyms).
'loses his head' means to remove the first letter.
'winner' with its initial letter taken away is 'INNER'.
'in the' is the link.
Can you help me to learn more?
(Other definitions for inner that I've seen before include "Internal - mental" , "Part of an archery target" , "red" , "Private, not expressed" , "Interior" .)