It is not a complete sentence because it has no subject; it doesn't say who or what is banging on the door.
Mary is banging on the door.
They are banging on the door.
The branches are banging on the door.
Who is banging on the door?
The grammar police are banging on the door.
Or you can make the 'banging on the door' the subject of a sentence, but it will need its own verb:
That banging on the door is annoying.
Banging on the door broke the window.
What about it? You need to use a complete sentence to tell us what you want to know.
The girl next door is the complete subject.
To change a sentence into passive the sentence must be active. 'Shut the door please' is not an active sentence, it is an imperative sentence, it has no subject. You could write something like this - You are asked to shut the door - but this is a bit awkward.
A simple subject is also a complete subject when it only contains one word.For instance: He went to the store. "He" is the only part of the subject at all. The rest of it is part of the complete predicate.
An imperative sentence has an implied subject. For example: "Stand up!" (meaning "[You] stand up!") "Don't open that door!" (meaning "Don't [you] open that door!")
'On the front door was pinned a note.' Is a complete sentence.
example of subject
No unless you break the door down while banging on it.
"Behind the door" could be a complete sentence, like in the answer to a question asking where something was.
Jenny was terrified because a grotesque zombie was at her front door and was banging and groaning trying to get inside her house.
No, "close the door" is a verb phrase, with "close" as the main verb and "the door" as the object of the verb. In this case, "the door" is the direct object of the verb.
hear
What about it? You need to use a complete sentence to tell us what you want to know.
put some oil on the corner of the door
By banging on their door and asking them to please quiet down.
Ask This Old House - 2002 Banging Pipes Installing Fiberglass Door 7-19 was released on: USA: February 2009
you call your mom and she says someones is banging on your rivals door