The most common and most likely answer to this crossword clue is the 4 plus 4 letter word OPEN FIRE
I've seen this crossword clue in The Guardian
O
P
E
N
F
I
R
E
More clues leading to the result OPEN FIRE
- Shoot from tree, in clear English
- Order to soldiers for some blazing coals
- One needing guard, perhaps, to start shooting
- Start attack where heat is on?
- Topless shoot that’s red hot
- One’s warmed by this shoot
- Start to pick off what Scouts cook on?
- Commence hostilities from which domestic sparks may fly?
- Not a closed range, so start shooting
- Begin hostilities in a hot place
Buddy explains!

The straight part
We know that "Warme/r/attack" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case warme/r/attack = open fire.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.