What would be a situation in which fights similar to this encounter in Romeo and Juliet Act 1, Scene 1 might occur today?
A fight like the brawl in the beginning of Romeo and Juliet might occur in a modern gang war.
From West Side Story, we might remember that Romeo and Juliet has modern connections. Unfortunately, feuds are not a thing of the past. In modern America, it is common for inner-city gangs to carve out territory and for families to line up on one side or the other. It is not unthinkable for a girl from one gang to be interested in a boy from another, because these kids live in the same greater neighborhoods and attend the same schools.
As Romeo demonstrates, not everyone is willing to fall in with the feud.
Here's much to do with hate, but more with love.
Why then, O brawling love! O loving hate! (Act 1, Scene 1, p. 16)
Romeo does not want to fight. He detests the brawl. While his family members and the Capulet family members seem willing to fight at a moment’s notice, he does not. Juliet likewise is not interested.
This often happens after gangs have been at war long enough for there to be significant casualties. At first, everyone wants to avenge so and so’s death. Then there comes a time when they are tired of the bloodshed.