The most common and most likely answer to this crossword clue is the 4 plus 2 plus 4 letter word BACK TO BACK
I've seen this crossword clue in The Guardian
B
A
C
K
T
O
B
A
C
K
Buddy explains!
The straight part
We know that "one after the other" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one after the other = back to back.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 BACK TO BACK mean?
BACK TO BACK adverb- With one's back facing that of somebody else.
- Consecutively; one after the other.
- A house with a party wall at the rear.
- Sequential or consecutive.
- With one's back facing that of somebody else.
- (of a house) Having a party wall at the rear