Baseball player's pet singer? (7)
I believe the answer is:
catcher
'baseball player's' is the definition.
(catcher is a kind of baseball player)
'pet singer?' is the wordplay.
'pet' becomes 'cat' (I've seen this in another clue).
'singer?' becomes 'cher' (Cher is a US musician).
'cat'+'cher'='CATCHER'
(Other definitions for catcher that I've seen before include "Baseball player - in the rye?" , "J D Salinger write ''The . . . . . . . in the Rye''" , "Famous Salinger novel ''The . . . . . . . In the Rye''" , "J D Salinger wrote 'The . . . . . . . in the Rye'" , "fisherman maybe" .)