Leader of lions died during Daniel's unorthodox convincing victory (9)
I believe the answer is:
landslide
'convincing victory' is the definition.
(I've seen this before)
'leader of lions died during daniel's unorthodox' is the wordplay.
'leader of' says to take the initial letters.
'died' becomes 'ds' (I can't justify this - if you can you should believe this answer much more).
'during' means one lot of letters goes inside another.
'unorthodox' indicates an anagram.
The first letter of 'lions' is 'l'.
'daniel' is an anagram of 'anlide'.
'ds' inserted within 'anlide' is 'andslide'.
'l'+'andslide'='LANDSLIDE'
Can you help me to learn more?
(Other definitions for landslide that I've seen before include "Overwhelming victory in election, or a natural disaster" , "Shifting of ground" , "Major earth movement" , "Overwhelming electoral victory" , "Movement at grass-roots level" .)