Brazilian Jiu-Jitsu has been proven to be an effective self dense system, however many of its detractors bring up the case of multiple attackers.
In reality, there is no perfect martial art against multiple attackers.
In this video, Rener Gracie adresses the question and offers a simple solution: Run.
If you cannot run, and are trapped, here are the three universal principles of self-defense as taught by the Gracie Academy, so you have a better chance of survival if you ever find yourself in a multiple attacker situation.
Principle 1: Diffuse the “Combative Energy” of the interaction.
Principle 2: Evade their attack with effective distance management.
Principle 3: Attack first and attack fast.