Defeating multiples is about controlling space and owning time. You have to keep moving, and keep moving in. You need to create chaos. Chaos is your friend. Attitude is everything, both yours and theirs. Dealing with real world violence demands that you think "crafty" rather than athletic or Martial. You have to learn to be cunning before you can deal with multiple attackers. Street criminals are not smarter than you, and they're usually not better educated than you. But they tend to be more cunning.
The principles of defeating multiples are attitude, entering space, time framing, landscaping, position, position, position, sight and accessing a weapon.
There is also a specific component and training to getting knocked to the ground while dealing with multiples.
When you fight someone man on man, in order to win you have to dominate that person. When fighting multiples you don't have to dominate anyone, you have to dominate the situation.