Supporter of monarchy: lot I say about getting behind king (8)
I believe the answer is:
royalist
'supporter of monarchy' is the definition.
(I've seen this before)
'lot i say about getting behind king' is the wordplay.
'about' indicates anagramming the letters.
'getting behind' means one lot of letters go next to another (some letters go behind others).
'king' becomes 'R' (abbreviation for rex, king in Latin).
'lot'+'i'+'say'='lotisay'
'lotisay' anagrammed gives 'oyalist'.
'oyalist' put after 'r' is 'ROYALIST'.
(Other definitions for royalist that I've seen before include "rightwinger?" , "Advocate of the principles of monarchy" , "For queen" , "Solitary kind of person who favours monarchy" , "Supporter of monarchy" .)