The most common and most likely answer to this crossword clue is the 8 letter word CYCLISTS
I've seen this crossword clue in The Guardian
C
Y
C
L
I
S
T
S
Buddy explains!
The straight part
We know that "Riders" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case riders = cyclists.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 CYCLISTS mean?
CYCLISTS noun- A person who rides a cycle, especially a bicycle, or who habitually engages in cycling.
- A user of the software language CycL.