Socialist supporting Queen is messed up (5)
I believe the answer is:
erred
'is messed up' is the definition.
'socialist supporting queen' is the wordplay.
'socialist' becomes 'red' (red is a kind of socialist).
'supporting' means one lot of letters go next to another (in a down clue, some letters go below others).
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'red' after 'er' is 'ERRED'.
(Other definitions for erred that I've seen before include "Made mistake, was incorrect" , "slipped up" , "was inaccurate" , "Was mistaken" , "Gone astray!" .)