Unfortunately Len's no hero (6)
I believe the answer is:
'hero' is the definition.
(I've seen this before)
'unfortunately len's no' is the wordplay.
'unfortunately' is an anagram indicator (a bad or unfortunate spelling).
'lensno' is an anagram of 'NELSON'.
(Other definitions for nelson that I've seen before include "Lady Hamilton's seafaring lover" , "British admiral, d. 1805" , "grip" , "British naval hero" , "Nile battle hero" .)