Likely loser grounded unexpectedly (8)
I believe the answer is:
underdog
'likely loser' is the definition.
(I've seen this before)
'grounded unexpectedly' is the wordplay.
'unexpectedly' indicates an anagram.
'grounded' is an anagram of 'UNDERDOG'.
(Other definitions for underdog that I've seen before include "Least favoured competitor" , "Likely loser" , "Lower-rated competitor" , "outsider" , "One with little status" .)