Trouble involving leader of Romantic poet’s fraternity (11)
I believe the answer is:
brotherhood
'fraternity' is the definition.
(I know that fraternity can be written as brotherhood)
'trouble involving leader of romantic poet's' is the wordplay.
'trouble' becomes 'bother' (synonyms).
'involving' means one lot of letters goes inside another.
'leader of' suggests taking the first letters.
'poet' becomes 'hood' (Thomas Hood, b799-b8he).
The first letter of 'romantic' is 'r'.
'bother' going around 'r' is 'brother'.
'brother'+'hood'='BROTHERHOOD'
(Other definitions for brotherhood that I've seen before include "association" , "Fraternity" , "union" , "Feeling of close kinship" , "Community" .)