The most common and most likely answer to this crossword clue is the 13 letter word CROSS-COUNTRY
I've seen this crossword clue in The Times
C
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C
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More clues leading to the result CROSS-COUNTRY
Buddy explains!

The straight part
We know that "Race" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case race = cross-country.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 CROSS-COUNTRY mean?
CROSS-COUNTRY noun- A running sport popular in US high schools, colleges, etc. where participants race over varying terrain (e.g. golf courses, roads, etc.) in approximately 5- to 10-kilometre races. Abbreviated XC.
- A phase of the equestrian sport of three day eventing, which the horse and rider travel over varied terrain and jump natural obstacles.
- Flight between two points or aerodromes using navigational techniques.
- From one side of a country to the other.
- Across countryside.
- Relating to cross country racing.
- (of data or research) Across countries.