This is not meant to pick on @Snailman, but there seems to be a relatively common belief that tournament modes should exclude extra balls.
There is no reason you can't run a tournament with extra balls.
So, no, on JJP games, setting a game to competition mode will not turn off extra balls. You can quickly achieve what you want (probably) by doing install novelty (turns off ebs, turns off all replays, sets specials to scores), install competition (same as a Stern, at least while I was there). Competition mode is active on Hobbit, and at the moment mostly makes mystery a useless award of always 1000 points. (This will change soon.) Other modes that use randomness should usually be the same as well, but in general there isn't a lot of game-changing randomness on Hobbit.
I would suggest you do use the install, however, because it will do a couple other things that you probably want, namely setting chase ball to OFF. Actually, that may be the only extra thing it does.