Opening race not without content (4)
I believe the answer is:
rent
'opening' is the definition.
(rent is a kind of opening)
'race not without content' is the wordplay.
'race' becomes 're' (I can't justify this - if you can you should give a lot more credence to this answer).
'without content' means to remove the middle letters.
'not' with its middle taken out is 'nt'.
're'+'nt'='RENT'
(Other definitions for rent that I've seen before include "Tear; lease" , "Money for hire - that's torn it" , "Torn, due to landlord" , "Tenant's payment" , "money demanded by letter" .)