The most common and most likely answer to this crossword clue is the 6 letter word PATRON
I've seen this crossword clue in Financial Times
P
A
T
R
O
N
More clues leading to the result PATRON
- Customer, old man, at marketplace
- Customer runs into no bar backwards
- Girl and boy’s benefactor
- Financial supporter recycled no art under pressure
- Customer exactly right and not upset
- Two little boys, one sponsoring another
- Country singer switching centre for proprietor
- Customer contributes little money to a pool of tips, mostly
- Sponsor a couple of boys?
- Paying customer to make severe criticism about rotten first half performance
Buddy explains!

The straight part
We know that "one sponsoring another" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case one sponsoring another = patron.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 PATRON mean?
PATRON noun- One who protects or supports; a defender or advocate.
- An influential, wealthy person who supported an artist, craftsman, a scholar or a noble.
- A customer, as of a certain store or restaurant.
- (Roman law) A protector of a dependent, especially a master who had freed a slave but still retained some paternal rights.
- One who has gift and disposition of a benefice.
- A padrone.
- A property owner, a landlord, a master. (Compare patroon.)
- To be a patron of; to patronize; to favour.
- To treat as a patron.