A ransom put together for Oxbridge blue, perhaps (7)
I believe the answer is:
oarsman
'oxbridge blue perhaps' is the definition.
(blue can mean an Oxford or Cambridge sportsperson)
'a ransom put together' is the wordplay.
'put together' indicates an anagram (put the letter together correctly).
'a'+'ransom'='aransom'
'aransom' is an anagram of 'OARSMAN'.
'for' acts as a link.
(Other definitions for oarsman that I've seen before include "A male small boat propeller" , "It's bordered by Libya and France" , "One in a row" , "A ransom (anag)" , "One in an eight?" .)