Support offered by HQ (4)
I believe the answer is:
base
This clue is a double definition.
'support' is the first definition.
(base is a kind of support)
'hq' is the second definition.
(I've seen this before)
'offered by' is the link.
(Other definitions for base that I've seen before include "'Foundation, bottom (4)'" , "Foot; ignoble" , "Starting point; wicked" , "Mil. operations centre" , "Mean - military installation" .)