The most common and most likely answer to this crossword clue is the 7 letter word KNOCKER
I've seen this crossword clue in The Daily Telegraph
K
N
O
C
K
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More clues leading to the result KNOCKER
Buddy explains!
The straight part
We know that "Hammer on the door?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case hammer on the door? = knocker.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 KNOCKER mean?
KNOCKER noun- A device, usually hinged with a striking plate, used for knocking on a door.
- A person who knocks.
- A critic; one who disparages.
- A person who knocks (denigrates) something.
- (usually in the plural) A woman's breasts.
- (especially Cardigan) A dwarf, goblin, or sprite imagined to dwell in mines and to indicate the presence of ore by knocking.
- A mechanical device in a pinball table that produces a loud percussive noise.
- A person who is strikingly handsome or otherwise admirable; a stunner.
- A large cockroach, especially Blaberus giganteus, of semitropical America, which is able to produce a loud knocking sound.
- A large, boulder-shaped outcrop of bedrock in an otherwise low-lying landscape, chiefly associated with a mélange.
- One who defaults on payment of a wager.