I would agree that you could dissuade a few monkeys from taking your sandwich. Animals don't particularly want to fight: even a "victory" could end badly if you live in a world without antibiotics, splints, or indeed any medical care.

On the other hand, if you backed five desperate monkeys into corner so that they think they are fighting for their lives, I think you'd fare much worse. I'd bet "punt attempts" sometimes end with the monkey clinging to your leg instead, chomping away at whatever they can reach (and even the molars can do some damage given the tremendous bite force).