Yes, actually. In all League-inspected and -approved fields, there are energy shields erected to disrupt distance attacks, protect spectators, and minimize damage to the stadium or gym. Higher-powered shields are additionally placed around spectator seating to prevent a pokémon or its attacks from passing through. (The weaker shields don’t prevent pokémon from flying right through, which allows them to use high-altitude moves such as Fly or Sky Attack … or, well. Fly out of bounds, in any case.)
Of course, this is secondary to proper training. Most trainers will teach their pokémon to stay within a field anyway, if only because of the rules concerning TKOs.
In other words, rest assured watching a battle from the stands is perfectly safe.
I don’t know. The Sinnoh league a while back had a super high powered battle between Cynthia and a previously unheard of trainer that was so dangerous they asked for everyone to move to the upper rows. Apparently it was considered safer to break the fire safety rules for capacity than it was to be within range of this fight.
They also never determined a winner either. The opponent forfeited despite being on even ground.
Well … true. If you hit the shields hard enough, there’s a slim chance that you’ll short them out, resulting in a failure. Restricting seating isn’t an ideal solution to this problem, but it is a precaution, in a sense, which is why I can almost understand why the League allowed that. Of course, it would make more sense to limit ticket sales, but on the other hand, when you have a champion battling, it tends to be a big event. (And frankly, Leagues sometimes look at ticket sales over certain other details—especially if you’re dealing with less popular leagues such as Sinnoh’s.)
The Pokédex According to Bill 