" Calling " Fair Ball

[Chess Ref]

Preconference Varsity Tourney I'M the PU. Runners on 2B +3B. Batter nails one down the LF line, close to the line. I, in all my newby glory, run out from behind the plate screaming like a madman "Fair Ball" "Fair Ball ". At least half the players involved, batter and runner on 3B stop in their tracks.
They thought I was screaming Foul Ball. Lucky for me BU was 20 year vet who knew what he was doing and cleaned the mess up for me. So I learned early on no calling Fair Balls. And I haven't done it again this year.
I understand SITCH is different but i learned the reason why we only call foul balls.