Sort of energy helping to keep support up (9)
I believe the answer is:
radiation
'sort of energy' is the definition.
'helping to keep support up' is the wordplay.
'helping' becomes 'ration' (I've seen this before).
'to keep' means one lot of letters goes inside another.
'support' becomes 'aid' ('aid' can be a synonym of 'support'**).
'up' is a reversal indicator (in down clue: letters go upwards).
'aid' reversed gives 'dia'.
'ration' placed around 'dia' is 'RADIATION'.
(Other definitions for radiation that I've seen before include "Harmful waves" , "Energy emitted by eg the sun" , "given out with mobile phones?" , "Nuclear emissions" , "Transmission of energy" .)