The most common and most likely answer to this crossword clue is the 2 plus 5 letter word EN GARDE
E
N
G
A
R
D
E
More clues leading to the result EN GARDE
- Grenade thrown in defensive position
- Be ready with foil, perhaps, having nearly finished wrapping cloth up
- Words of warning from gentlemen gardening
- Translation of ‘Danger!’ before tip of epée is seen?
- Warning fencing’s about to start blocking neighbouring gardens
- Opening position heard to be vigilant
- End rage in battle call to alert swordsman
- Fighting words: grenade exploding!
- Warning posted in kitchen garden
- Savage angered, prepare for a fight
Buddy explains!

The straight part
We know that "Opening position" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case opening position = en garde.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.