Fist Or Open Hand ...
 

Dribbler closely defended very near the sideline. Dribbler barely steps on the boundary and is (unintentionally) pushed a split second later.

The synapses in my brain get momentarily tangled up and I come up with a fist that I immediately (while my hand is still in the air) change to a open hand and call "Red" and point the other way.

Once the coach sees that I'm not reporting a foul, he politely asks me, "Didn't you put up a fist for a foul?".

Over forty-plus years, I've probably done this dozens of time (fist instead of an open hand, or open hand instead of a fist, and then immediately change to what I really wanted to call) and have never been caught.

Short discussion with the coach settled it immediately (out of bounds came first), but I'm still surprised that I got caught.

Some coaches are smarter than we believe them to be.