What I posted earlier might seem hard to imagine. However in truth the well thrown spitter breaks so late and so sharply downward that there is really no mistaking what it is once you have seen it and know what to look for.
In fact later in Gaylord Perry's career it got to the point where there was no sense in announcers hiding what was going on. Some of them would in a very matter of fact tone, just in the flow of the broadcast identify the pitch as the spitter just as if they were announcing a curve ball or some other pitch. For the most part the umps had given up trying to find where Gaylord had the stuff hidden that day and managers stopped trying to get umps to look for it. That's one of the things that annoys me about this. These are baseball people. They know what a spit ball looks like.