Before you do your show you have to sell your show to the people walking by.
The Bally is a scripted crowd building routine, meant to stop people, to crowd them together, and tell them what you do.
It's like a live pre-show trailer, to give the people an idea of what you do, build interest, and gather them together to get ready for the show.
It should be scripted in such a way as to be repeatable, in case nobody stops the first time.
This routine is just like any magic routine you do, but this routine is designed to get people to stop and watch.
It has a beginning, a middle and an end.
You repeat this, if need be, over and over again, until you get the desired amount of people you need to get a show together, depending on the size and length of the show you do.
If you do a short sidewalk show 5-12 minutes long your bally could be a minute or two long, but if you do a big circle show it could run like ten minutes or more.
This routine should be your strongest routine because it's the one that breaks the ice and introduces your character and skills.
It needs to have stopping power, and build rapport.
Once again it is a scripted repeatable routine with a beginning, middle and end that is designed to stop and gather people.
A couple extra notes: project further than who is already stopped and “break the walls”. Appear to be larger than your confined performing area, which falls under movement, setting you up to have a larger impromptu theatre.