In short, they are bullies.
And, like all bullies, they are brave in a crowd. Faced with someone who isn't afraid of them, and is comfortable with violence, and the balance shifts. An example:
Now, to be fair, the gentleman wielding the baton wasn't particularly skilled. He seemed to make the, all too common, mistake of believing that his weapon bestowed upon him competence. As if the baton were a magic talisman that would give him super powers against a determined foe.
Even worse, the defender that threw the punch seemed to be surprised that his strike was as effective as it was. His form left something to be desired, but the result speaks for itself.
I'm not sure what the woman on the left was trying to accomplish. Perhaps, upon seeing her champion so easily downed, she was offering to bear the victor's children. More likely, she was begging him to not give her friend the educational beatdown he so richly deserved.
I suspect that, were the Dollar-Store Ninjas met with this type of response more often, they would quickly learn to mind their manners.