Go to a college game (and many high school) games and you will undoubtedly hear multiple people from the defensive team yell “RUNNER!!” when a runner takes off to steal. My son’s 11 year old team is just starting to learn this concept. For them, this is the first year runners can take leads and steal on the pitcher’s first move to the plate. In previous years, runners could not steal until the ball crossed home plate. On every pitch, the catcher would come up ready to throw and see for himself whether or not he had to. That’s all gone now.
Catchers have to know immediately when the runner takes off. If a right handed batter is up then very often the catcher will see the runner break from his peripheral vision. This is also the case with runners stealing third base. However, this not always possible in other situations.
One situation is when a lefty is batting. The batter blocks his vision of first base so someone has to let him know when the runner takes off. Typically this is the first baseman who can yell “RUNNER!!” since he is holding the runner on and has the ability to see the runner’s actions.
Another situation is a delayed steal. In this situation (even when there is a right handed batter), the runner takes off when the catcher is focused on receiving/blocking the ball and cannot always see the runner turn his shuffles into a sprint. The first baseman cannot see what happens either since he will be facing home plate after his “shuffle off on the pitch” and cannot see the runner’s actions anymore.
All these situations require teams to create a habit of yelling “RUNNER!!” on the part of any player and/or coach on or off the field when runners take off. Teams cannot assume the catcher knows. Everyone who sees it has to yell.
This is also a good way to keep your bench players engaged and watching the game. If they don’t yell, they are not engaged.
Good teams do a lot of little things correctly. This is one of them.