The most common and most likely answer to this crossword clue is the 7 plus 3 letter word WELCOME MAT
I've seen this crossword clue in The Guardian
W
E
L
C
O
M
E
M
A
T
Buddy explains!
The straight part
We know that "one trampled on outside the door" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one trampled on outside the door = welcome mat.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.