Old instrument to be buried in sports ground (5)
I believe the answer is:
rebec
'old instrument' is the definition.
(I've seen this in another clue)
'be buried in sports ground' is the wordplay.
'buried in' means one lot of letters goes inside another (inserted letters get buried).
'sports ground' becomes 'rec' (abbreviation for recreation ground).
'be' placed inside 'rec' is 'REBEC'.
'to' acts as a link.
(Other definitions for rebec that I've seen before include "Old stringed instrument" , "Mediaeval stringed instrument" , "Medieval bowed instrument" .)