If you're ever attacked by the 'street'...
...Aikido will teach you how to resolve the matter peacefully. Anyone, who has fallen down, can see the benefit of that!
There are myriad's of reasons why individuals - regardless of affiliation - behave this way, which I think is self-evident upon reflection. The quick answer is this:
'For those who understand, no explanation is necessary; for those who do not understand, no explanation will suffice'.