Agreement rules refer to the agreement between verbs and subjects in a clause, including the subjects that are collective nouns (such as team, group, staff, and family).
In American English, the subject-verb agreement pattern is determined by the singular or plural form of the collective noun. Thus, it is more likely that the above mentioned nouns will be used with a singular verb (e.g., the team is ready for the game), while such names of sport teams as The Angels, The Broncos, The Cowboys will take a plural verb (e.g., the Broncos have won again).
In British English, the use of the verb (singular or plural) is more likely to be determined by the meaning of the collective noun. Thus, if one perceives a family as one unit, singular verb is used (e.g., my family is big), and if one refers to the family as a group of individuals, plural verb is required (e.g., the whole family have gathered at the table).