If something such as a competition or an election is too close to call, it is not possible to predict who will win because it seems likely to be won by only a very small margin.
[journalism]
In the Senate, the count is too close to call at this point.
See full dictionary entry for close
too close to call in British English
(of the outcome of a competition, election, match, etc) unable to be predicted
See full dictionary entry for call
Examples of 'too close to call' in a sentence
too close to call
In all three states the results at this stage are too close to call.