The most common and most likely answer to this crossword clue is the 8 letter word STOWAWAY
S
T
O
W
A
W
A
Y
More clues leading to the result STOWAWAY
- Unauthorised passenger was to, after changing course
- A white toy was unexpectedly found as an illegal item on board
- Someone taking off with airline without approval? Yes, primarily
- One not having paid to travel, bailiffs finally take vehicle to pound
- Clandestine boarder observed circling tug, always
- Son to drag off fare dodger?
- One in a hold ultimately has to pull continuously
- Secret tripper‘s pack?
- Fare-dodger ‘s stash
- Illegal passenger‘s expressions of pain and disgust going into hold
Buddy explains!

The straight part
We know that "sneaky rider" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sneaky rider = stowaway.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 STOWAWAY mean?
STOWAWAY noun- A person who hides on board a ship, train, etc. so as to get a free passage.