A real fight is a fight that does not take place in-game, including the kind where fists actually fly.
It’s just a game, you should really just relax.
There are plenty of reasons players feel compelled to go at it: simply losing and messing up the score; getting challenged, hence getting distracted from the story; complaining that someone is a chicken; even snapping at the opponent or a spectator can start a fight.
Among the worst causes are attempts to get revenge on those who go on a newbie beatdown in order to play among one’s own circle, or those who challenge overbearingly in great numbers, or those who make threats.
At any rate, there is no good excuse for committing the crime of assault, and in the worst cases, the police get involved.
Usual consequences include being banned from the premises, and getting arrested if things get very out-of-hand. It’s what people get for being infantile.
Moreover, it disturbs uninvolved people, such as other customers and the employees; in other words, it is an utterly disgraceful thing to do.
Real fights are one of the primary reasons some hold fighting games, video arcades, and/or games in general in ill regard, and is connected in the minds of some to the general decline of the arcade.
Although it doesn’t happen too often nowadays, there were many highly-publicized real fight incidents in the 1990’s, so some people still hold prejudices from what they know of them. The relatively subdued game centers of today have suffered from this reputation in no small way.