Critical party supporting gutless leader (5)
I believe the answer is:
grave
'critical' is the definition.
('grave' can be similar in meaning to 'critical')
'party supporting gutless leader' is the wordplay.
'party' becomes 'rave' (I've seen this before**).
'supporting' means one lot of letters go next to another (in a down clue, some letters go below others).
'leader' says to take the initial letters.
The first letter of 'gutless' is 'g'.
'rave' put after 'g' is 'GRAVE'.
(Other definitions for grave that I've seen before include "Sober" , "foreign accent" , "Solemn - burial place" , "of importance" , "Serious in cemetery?" .)