Picture this, a dimly lit public space at dusk with light to very light density of people,

you are alone, walking to your car, or the bodega,

there is someone there to stick you for your paper and smartphone,

but wait, now PICTURE THIS:

you are walking in the same public space with the same conditions as in the first description,

but now you are bouncing a tennis ball as you walk. you bounce it, catch it and bounce it again, the entire time you are walking?

who would attack you now? no one.

why?

few reasons to consider:

just by walking at a steady pace and confidently bouncing the ball as you walk, you show a high level of hand eye coordination and give off a hint of athleticism; you are an active person, not weak prey,

if all else fails, the other guy doesn't know your arm strength; what if you will throw the ball at his face while he is about to strike? it can give you key moment to escape,

I'm just glad you survived the cream.

Acctually not a bad tip, although I don't think it adds much of an intimidation element to their character.
From a practicallity stand point, the ball's making noise while you're bouncing it, drawing attention. Muggers are less likely to want to go up to someone other people are looking at.