The most common and most likely answer to this crossword clue is the 10 plus 5 letter word DISCOVERED CHECK
I've seen this crossword clue in The Guardian
D
I
S
C
O
V
E
R
E
D
C
H
E
C
K
More clues leading to the result DISCOVERED CHECK
Buddy explains!
The straight part
We know that "Board move" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case board move = discovered check.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.