Bobby is firm, yet soft (3)
I believe the answer is:
cop
'bobby' is the definition.
(I've seen this in other clues)
'firm yet soft' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'yet soft' becomes 'p' (musical abbreviation for 'piano', soft. I am not sure about the 'yet' bit.).
'co'+'p'='COP'
'is' is the link.
Can you help me to learn more?
(Other definitions for cop that I've seen before include "Policeman (slang)" , "An American policeman" , "Policeman (colloq.)" , "Short policeman" , "Policeman (sl)" .)