Jamieson, Fausset and Brown on 1 Samuel 25:10-12

10-12. Nabal answered David's servants, ... Who is David? &c.--Nabal's answer seems to indicate that the country was at the time in a loose and disorderly state. David's own good conduct, however, as well as the important services rendered by him and his men, were readily attested by Nabal's servants. The preparations of David to chastise his insolent language and ungrateful requital are exactly what would be done in the present day by Arab chiefs, who protect the cattle of the large and wealthy sheep masters from the attacks of the marauding border tribes or wild beasts. Their protection creates a claim for some kind of tribute, in the shape of supplies of food and necessaries, which is usually given with great good will and gratitude; but when withheld, is enforced as a right. Nabal's refusal, therefore, was a violation of the established usages of the place.