The different responses to the initial post point to some of the variables one would need to consider after one defended oneself. Since we don't know what "it" was that started the confrontation, it opens "it" up to more variations. But lets take a couple.
But first the caveat, this is a question that will be answered differently around the country. In some places, for example, there is a recognition of the concept of "fighting words." That is, the courts in these jurisdictions would view certain comments directed toward another person as intended to elicit physical confrontation. In other places, the same words would not be sufficient provocation to enter into combat.
Most places will look for a person to avoid combat and expect, at minimum, that before one defends oneself, one is in reasonable (there's a word that could open up a whole thread) fear of emminient harmful or perhaps offensive contact. (Harmful might be a person attempting to hit you, offensive might be a person engaging in unwanted touching). In most places, there does not need to be actual contact before one may defend oneself, the reasonable fear allows one to take defensive action. For example, it is unlikely a court would expect a person to actually allow him or herself to be cut by a knife before defending him or herself. A person brandishing a knife in a threatening way and making movement to cut would typically justify a defensive response.
In most places, the court is also going to look to see if the person defending him or herself took advantage of an opportunity to escape the confrontation. Even if you are in reasonable fear, if you have a reasonable means of avoiding confrontation, the court would expect you to take the non confrontational out. Again, your avenue of escape needs to be reasonable. You are not expected, for example, to leap from a height or put yourself at further risk by your escape.
As some have pointed out, one may also defend another, but since this post is getting much longer and more complicated than I would like, I will save that for some other time.
Again, in our country, it is the sovereign states (or commonwealth if you happen to be in say, Massachusetts) that in theory control the police power. One's civil and criminal liability in a self defense situation will typically be governed by the law of the state where the confrontation takes place. In other words, know the local rules. In some areas of the country, getting drunk and getting in a fight is viewed as fairly normal recreational activity. In California, it gets you arrested, and if you have any money, it gets you involved in the wonderful word of civil litigation. In Texas, well lets not go there.
The guys in the dockers should have saved themselves the hassle they are both in for and settled their differences with a game of horse.