The most common and most likely answer to this crossword clue is the 8 letter word HEADLOCK
I've seen this crossword clue in The Daily Telegraph
H
E
A
D
L
O
C
K
More clues leading to the result HEADLOCK
Buddy explains!

The straight part
We know that "a grip" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a grip = headlock.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 HEADLOCK mean?
HEADLOCK noun- A wrestling move where the attacker puts their arm tightly round their opponent's head, which the opponent can't easily escape from.