After half time, she's gone wrong (6)
I believe the answer is:
imogen
'after half time' is the definition.
The definition suggests a singular noun which matches the answer.
'she's gone wrong' is the wordplay.
'she' becomes 'im' (I can't explain this - if you can you should give a lot more credence to this answer).
'wrong' is an anagram indicator.
'gone' with letters rearranged gives 'ogen'.
'im'+'ogen'='IMOGEN'
Can you help me to learn more?
(Other definitions for imogen that I've seen before include "Girl's name; go mine (anagram)" , "Character 8 [OF SHAKESPEARE]" , "Woman" , "child of a king" , "identity of Cymbeline's daughter" .)