Tidy elf I spoilt shows loyalty (8)
I believe the answer is:
fidelity
'loyalty' is the definition.
(I've seen this before)
'tidy elf i spoilt' is the wordplay.
'spoilt' is an anagram indicator.
'tidy'+'elf'+'i'='tidyelfi'
'tidyelfi' is an anagram of 'FIDELITY'.
'shows' is the link.
(Other definitions for fidelity that I've seen before include "Honesty" , "Devotion" , "Faithfulness" , "Tidy file (anag)" , "The quality of being faithful" .)