Yesterday I stood on the side and watched a 4.0 doubles match (social). After a game was over, I told the server that every one of his serves was a FF. He was caught by surprise and just stood there staring at me, and I thought oh oh time to make a fast retreat. Then his partner "comes out"" and says I have seen you FFing all the time, and then proceeds to explain in detail how his foot comes forward and catches the line before the serve!
His partner had bottled it all in before this and he let it all come out when given the opportunity.