The most common and most likely answer to this crossword clue is the 9 letter word SPIN-OFFS
I've seen this crossword clue in The Times
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More clues leading to the result SPIN-OFFS
Buddy explains!

The straight part
We know that "By-products" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case by-products = spin-offs.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 SPIN-OFFS mean?
SPIN-OFFS noun- An offshoot.
- An incidental benefit or unexpected pay-off.
- By-product.
- A fictional work where the protagonist was introduced in a preceding work or at least shares the same setting, often in a different aspect.
- The formation of a subsidiary company that continues the operations of part of the parent company; the company so formed.