One of the things I encountered early on in my habit of running several times a week?
Aggressive dogs.
I live rural, which I mostly love, but for some reason, many people who live rurally don't understand that even in the county there IS a Leash Law.
They also seem to not realize that dogs are naturally territorial and protective. Hence, when someone (kid, adult, whomever) is walking or running on the public roadway, that dog is going to go nuts.
Sometimes they try to chase, growl, bite and attack pedestrians.
The answer I got when I asked veteran runners what I should do? Get runner's mace.