A poor loser full of love can, under pressure (7)
I believe the answer is:
aerosol
'can under pressure' is the definition.
(pressurised can)
'a poor loser full of love' is the wordplay.
'poor' indicates an anagram.
'full of' is an insertion indicator.
'love' becomes 'o' (love means zero in tennis).
'loser' with letters rearranged gives 'erosl'.
'erosl' enclosing 'o' is 'erosol'.
'a'+'erosol'='AEROSOL'
(Other definitions for aerosol that I've seen before include "It dispenses liquid in a fine spray" , "Sprayer" , "Air-spray" , "Liquid in a container under pressure" , "fog?" .)