Final United competition acquiring new stamina (9)
I believe the answer is:
endurance
'stamina' is the definition.
(I've seen this before)
'final united competition acquiring new' is the wordplay.
I cannot quite understand how this works, but
'final' could be 'end' (synonyms) and 'end' is present in the answer.
'united' could be 'u' (as in Man U, English football team) and 'u' is present in the answer.
'new' could be 'n' (abbreviation as in New Testament NT) and 'n' is located in the answer.
'competition' could be 'race' (race is a kind of competition) and 'race' is located in the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for endurance that I've seen before include "Ability to withstand prolonged hardship" , "Lasting nature" , "Tenacity" , "Bearing" , "Patient toleration" .)