In the play 'Romeo and Juliet' by William Shakespeare, the author shows us two dynasties or famous aristocratic families who both have a bevy of servants and courtiers to help run their households. For reasons lost in the mists of time, the two families hate each other and are deriving enjoyment and staisfaction from carrying on the feud, master to master, servant to servant. Basically, it has become a habit and that is all - for now! Soon, we are going to see where it all could, and does, end. Many psychologoists of today would say that groups of young men have a basic drive to fight - and the feud merely gives them an excuse - much like gang culture today.
In Shakespeare's Romeo and Juliet, Sampson and Gregory, who belong to the Capulet family, fight with the Montagues simply because they are Montagues. Their motivation is revealed in their dialogue before they come face to face with the Montagues.
Sampson and Gregory are goading or teasing each other and Gregory teases Sampson by saying that he is slow to be moved to strike with his sword, and Sampson replies:
A dog of the house of Montague moves me.
Sampson not only says that he will be moved to fight by a Montague, but he calls the Montagues dogs at the same time.
A line or two later Sampson says that he will "push Montague's men from the wall and/thrust his maids to the wall." Gregory replies by saying that the quarrel is only between their masters and the masters' men (not the maids), but Sampson replies:
Tis all one. I will make myself a tyrant.
When I have fought with the men, I will be cruel
with the maids--I wil cut off their heads.
The Montagues and Capulets are involved in a feud. Sampson and Gregory hate the Montagues for no better reason than that.
For fun, it's something to do. This is just what they did when they ran into a servant or any other person from the opposing side.
If you listen to the Prince's speech later, he refers to 3 civils brawls that have disturbed the peace in the streets, so obviously it happens a lot.
Within their words in working to make a decision whether to fight or not, their discussion is playful. This opening scene is intentionally comedic, even if it doesn't feel like it. These two guys are talking about fighting the Montagues' women (or madiens... more specifically madienheads... look it up and read again for a little humor). They have fun talking about their 'tools' and naked 'weapons'. This fight scene gives them room to have had this decision discussion beforehand which is rather funny with the right frame of mind. (Or maybe that's the wrong frame of mind)
In my opinion, there are two major reasons why they fight with the servants of the Montagues. First, they are hot heads. They are presumably young and young men tend to have hot tempers. Second, they belong to opposite "gangs." Whenever they see someone from the rival "gang" they are likely to end up having a fight.
Before the Montagues even come along, Sampson is already talking about wanting to fight. This shows that the fight isn't from any real provocation -- it's just because of the two factors I cited above.