The most common and most likely answer to this crossword clue is the 9 letter word SPEEDSTER
I've seen this crossword clue in Financial Times
S
P
E
E
D
S
T
E
R
Buddy explains!

The straight part
We know that "Boy racer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case boy racer = speedster.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 SPEEDSTER mean?
SPEEDSTER noun- One who is noted for being very fast.
- A person who speeds (drives fast).
- A vehicle or other device used for racing.