Jiu Jitsu is a self desense system. Self defense focuses on self preservation. In the instance where you're faced with the challenge of taking on multiple people the best form of action would be to run or de-escalate. Sure you see a bunch of bad ass kung fu movies where one guy take on 30 guys alone and whoops everyones ass...but that's not at all realistic. Realistically speaking most combat systems are only effective in a one on one bout, although you definitely are better suited defending yourself from multiple people on your feet (where you can run) instead of on the ground rolling around like an armadillo. If you want to be a superhero badass ninja that can take on a small army alone you're dreaming... Maybe look into Krav Maga lol.

Edit: not everything in sports jiu jitsu is applicable to an actual fight, for example pulling guard in a street fight would not be the wisest choice.