Thug heading for real trouble in Goa (7)
I believe the answer is:
gorilla
'thug' is the definition.
(I've seen this before)
'heading for real trouble in goa' is the wordplay.
'heading for' indicates taking the first letters.
'trouble' becomes 'ill' (synonyms).
'in' indicates putting letters inside.
The first letter of 'real' is 'r'.
'r'+'ill'='rill'
'rill' placed inside 'goa' is 'GORILLA'.
(Other definitions for gorilla that I've seen before include "Chest-beating primate" , "Powerful great ape" , "Largest living primate" , "A large powerful African ape" , "The biggest ape" .)