The most common and most likely answer to this crossword clue is the 5 plus 3 plus 7 letter word BLOOD AND THUNDER
I've seen this crossword clue in The Daily Telegraph
B
L
O
O
D
A
N
D
T
H
U
N
D
E
R
More clues leading to the result BLOOD AND THUNDER
Buddy explains!
The straight part
We know that "Unrestrained and violent action" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case unrestrained and violent action = blood and thunder.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.