Mm... Not usually? It's not common for troublesome wild Pokémon to wander into cities, but it happens from time to time - like I mentioned, us Gym Leaders are usually called on when that happens. Apart from that, they usually stay away from human settlements.

[ Hammerlocke's large walls make it especially uncommon, but there's been a few times where Flying Pokémon have had squabbles over territory near the castle towers. other leaders like Milo have to keep a closer eye out for trouble, thanks to their cities being wide open. ]

But if it's the other way around and you're out on their turf without a way to protect yourself, that's just asking for trouble.