Greeks struggling in heat since about noon (9)
I believe the answer is:
athenians
'greeks' is the definition.
(Athenian is an example)
'struggling in heat since about noon' is the wordplay.
'struggling' indicates anagramming the letters (the letters struggle or wriggle into a new form).
'since' becomes 'as' (both can mean 'because').
'about' indicates putting letters inside.
'noon' becomes 'n' (abbreviation for noon).
'as' going around 'n' is 'ans'.
'in'+'heat'='inheat'
'inheat' is an anagram of 'atheni'.
'atheni'+'ans'='ATHENIANS'
(Other definitions for athenians that I've seen before include "foreign guests perhaps" , "Foreign citizens" .)