So i watch shows and videos of Pokémon battling in arenas surrounded by audiences and I’ve always wondered how the people never get hit by some strayin Pokémon moves. Is there invisible barriers of some kind or is there another explanation?

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.