Lethargy from United playing sport outside (6)
I believe the answer is:
stupor
'lethargy' is the definition.
(I've seen this in another clue)
'united playing sport outside' is the wordplay.
'united' becomes 'U' (abbreviation as in Man U for Manchester United).
'playing' indicates an anagram.
'outside' is an insertion indicator.
'sport' anagrammed gives 'stpor'.
'u' inserted inside 'stpor' is 'STUPOR'.
'from' acts as a link.
(Other definitions for stupor that I've seen before include "Coma - lassitude" , "State of being dazed or numb" , "result of too much snow?" , "State of near unconsciousness" , "Insensible state" .)