The most common and most likely answer to this crossword clue is the 7 letter word RUBDOWN
I've seen this crossword clue in The Times
R
U
B
D
O
W
N
Buddy explains!
The straight part
We know that "Sand/treatment post-exercise" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sand/treatment post-exercise = rubdown.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 RUBDOWN mean?
RUBDOWN noun- A quick, energetic massage.