Reindeer quietly scampered round sports ground (7)
I believe the answer is:
prancer
'reindeer' is the definition.
(one of Santa's)
'quietly scampered round sports ground' is the wordplay.
'quietly' becomes 'p' (p for piano and quiet).
'scampered' becomes 'ran'.
'round' says the letters should be written backwards.
'sports ground' becomes 'rec' (I've seen this in other clues).
'rec' reversed gives 'cer'.
'p'+'ran'+'cer'='PRANCER'
(Other definitions for prancer that I've seen before include "Spirited horse" , "One of Santa's reindeers" , "A lively horse" , "Xmas reindeer" , "Sleigh-puller" .)