Old player's son very good at cricket practice (6)
I believe the answer is:
spinet
'old player's' is the definition.
(historical musical instrument)
'son very good at cricket practice' is the wordplay.
'son' becomes 's'.
'very good' becomes 'pi' (I've seen this in other clues).
'at' means one lot of letters go next to another.
'cricket practice' becomes 'net' (I've seen this before).
's'+'pi'+'net'='SPINET'
(Other definitions for spinet that I've seen before include "Small 12" , "Harpsichord-like keyboard instrument" , "Instrument resembling a small harpsichord" , "Instep (anag)" , "Step in with old musical instrument" .)