[CJP]

As a newer official, all I have ever known is to signal to stop the clock with the open hand first then go to the thumbs. The first year I officiated, local association head officials made this a point of emphasis for everyone. I never read into it so I didn't know any better. This past year I moved and all of my partners went straight to the thumbs. Yes, there were double whistles, I don't recall a time where we had conflicting calls though but the potential is there. After discussing this with my new partners, a couple of them agreed that it made more sense to go with an open hand first. For me, it is a habit - either an open hand or fist on a whistle and I may never break that habit.