The most common and most likely answer to this crossword clue is the 9 letter word OFFSEASON
I've seen this crossword clue in The Daily Telegraph
O
F
F
S
E
A
S
O
N
More clues leading to the result OFFSEASON
Buddy explains!

The straight part
We know that "less popular period" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case less popular period = offseason.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 OFFSEASON mean?
OFFSEASON noun- That part of the year when business is most slack and there are fewest clients or visitors
- Period of time when regular competitions are not being held, or when an athlete is not participating in competitions.