Do a search on “reasonable expectation of privacy”
Essentially, if you’re at a public event on public property, people attending likely have none. (Exceptions may apply – always consult a qualified legal professional to determine your potential liability)
But generally, at the public school little league game, feel free to pan the crowd.
If you’re at a ticketed event on private property – like a concert – even if it’s open to the public, it gets dicier. This is why events sometimes print a presumptive release on their tickets and sometimes post public notices that taping is going on and that if you attend, you’re agreeing to waive your privacy rights for that event.
One reason you often see blurred faces in videos is that the subject of the video might be something that could cast an innocent bystander in an unfavorable light. For example, if a non-customer happens to be leaning on the wall outside an adult bookstore – or is leaving a restaurant where the crew of some CHEATERS like program is shooting on a public street, someone could argue that showing their likeness in that context implies that they’re participants – so out comes the blur filter.
The bottom line is that anyone can sue anyone for anything. So learning how to protect yourself from the threat of litigation is not only smart – it’s often worth spending money to do properly.
YMMV.
Good luck.