Set against hot wheel, alien gets headgear (4,6)
I believe the answer is:
pith helmet
'headgear' is the definition.
(pith helmet is a kind of headgear)
'set against hot wheel alien' is the wordplay.
'set against' is a charade indicator (letters next to each other).
'hot' becomes 'pith' (I am not sure about this - if you are sure you should believe this answer much more).
'wheel' becomes 'helm' (wheel on a ship).
'alien' becomes 'et' (extra terrestrial).
'pith'+'helm' is 'pithhelm'.
'pithhelm'+'et'='PITH HELMET'
'gets' is the link.
Can you help me to learn more?
(Another definition for pith helmet that I've seen is " sun-shield".)