The most common and most likely answer to this crossword clue is the 8 letter word JOYRIDER
J
O
Y
R
I
D
E
R
More clues leading to the result JOYRIDER
- Transport add-on, one given to appropriate vehicles?
- One taking car from girl – a legal stipulation
- Girl requiring qualification, reckless driver
- Lawless controller of estate, say?
- Criminal only disheartened with condition attached by judge initially
- Car thief found on the merry-go-round?
- Judge with additional statement about lad losing head as a criminal
Buddy explains!

The straight part
We know that "Lawless controller of estate, say?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lawless controller of estate, say? = joyrider.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.