Unsucccessful person left incredibly sore (5)
I believe the answer is:
loser
'unsucccessful person' is the definition.
I can't judge whether this defines the answer.
'left incredibly sore' is the wordplay.
'left' becomes 'l' (common abbreviation).
'incredibly' is an anagram indicator.
'sore' is an anagram of 'oser'.
'l'+'oser'='LOSER'
Can you help me to learn more?
(Other definitions for loser that I've seen before include "One who is habitually unsuccessful" , "Failed competitor" , "One frequently failing" , "One not winning" , "Someone who fails consistently" .)