The most common and most likely answer to this crossword clue is the 4 plus 3 plus 2 letter word TOSS FOR IT
I've seen this crossword clue in Financial Times
T
O
S
S
F
O
R
I
T
Buddy explains!
The straight part
We know that "Call for heads, possibly" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case call for heads, possibly = toss for it.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.