The most common and most likely answer to this crossword clue is the 9 letter word UNBRIDLED
I've seen this crossword clue in The Daily Telegraph
U
N
B
R
I
D
L
E
D
Buddy explains!

The straight part
We know that "With no restraints" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case with no restraints = unbridled.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.
What does UNBRIDLED mean?
UNBRIDLED verb- To remove the bridle, and other tack, from (a horse or other animal).
- To remove restraint from.
- Not fitted with a bridle.
- (by extension) Without restraint or limit.