Expression "hard one to call"

[Schoolofelectro]

Hello.
If someone says 'It's hard one to call', then does he or she mean 'It's hard to decide'?
I guessed so but my dictionary does not seem to say that 'call' has a meaning of 'decide'.
Thank you in advance!

[Skrej]

Note that the correct phrase is "It's a hard one to call".

Yes, this is an idiom meaning 'hard to decide, or difficult to make a judgment about'.

The idiom comes from the world of sports, where referees have to make judgments and decisions about rules or violations during the game. Those decisions are known as 'calls'.

<edit>My dictionary (Merriam Webster) lists the following definition for 'call' that fit this idiom.

j : to rule on the status of (as a pitched ball or a player's action) *call balls and strikes* *call a base runner safe*
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[Schoolofelectro]

Thank you for your explanation and the correction as well!
Your reply helped a lot.
Maybe I have to add Merriam Webster to my dictionary collection :)