The most common and most likely answer to this crossword clue is the 6 letter word RIOTER
I've seen this crossword clue in Financial Times
R
I
O
T
E
R
More clues leading to the result RIOTER
- With order originally maintained, author losing head as one joining the fray?
- Insurrectionist in city about to start uprising
- One is disturbing the peace, as trio plays with soap from America
- Troublemaker in port starts to turn everyone rebellious
- Letters from Mario terrorise the insurgent
- Troublemaker meets end mostly near port
- Rigorous imprisonment further disheartened troublemaker
- He revels in corruption engulfing current head of state
Buddy explains!

The straight part
We know that "He revels" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case he revels = rioter.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.