Half of find submerged in ancient city gives diver problem (3,5)
I believe the answer is:
the bends
'diver problem' is the definition.
(condition experienced by divers)
'half of find submerged in ancient city' is the wordplay.
'half of' indicates taking half.
'submerged in' means one lot of letters goes inside another (I've seen this in other clues).
'ancient city' becomes 'thebes' (ancient Greek city).
'find' cut in half is 'nd'.
'nd' placed inside 'thebes' is 'THE BENDS'.
'gives' is the link.
(Other definitions for the bends that I've seen before include "Problem for divers" , "Decompression sickness (suffered by divers)" , "Diver's ailment" , "Sickness which drivers must watch out for" , "A risk for divers" .)