Blocked out on fair/foul call

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What do you call when you get blocked out on a fair/foul call? Line drive down 1st base line. I line up to call it but batter/runner running in fair territory moves to running lane just as ball hits ground. Also, first basemen of course runs over to see if it's fair/foul as well.

I make "no" call cuz I simply cannot see it. Because I make "no" call it's assumed to be fair by defense and they attempt a play. Of course, I hear afterward it's foul.

I left it fair. Was I right?

By the way, there was no time to get anywhere but looking down the line from behind the plate.