There is the general consensus that being outnumbered in an altercation is a death sentence unless you flee. While that is generally the case, it is also not always the case. The key is to have an equalizer such as a self defense weapon of choice.
In the event of a group altercation where one person is outnumbered, the key to winning is not just skill, but also the way the other group attacks. This is affected by their mental state of mind. If the person is a big intimidating man with long reach, the individuals of the group would likely be somewhat scared to attack. Taking advantage of this can easily result in the loss of the group despite the number advantage.