Collective nouns in English
Collective nouns denote a group of persons, family, team, etc. They always occur in the singular form (staff, crew) except for folk, committee, which are also used in the plural: folks, committees.
1. Some collective nouns are followed either by a singular verb (when they refer to a whole group) or by a plural verb (when they refer to individual members of the group):
e.g. clergy, gentry
The clergy constitutes a social group.
Fifty of the clergy were present at the meeting.
2. Some collective nouns always take a plural verb: e.g. cattle, police
The police have found the wanted murderer. 
Reference to individual members of the group is made by: 
e.g. ten head of cattle or five police (policemen).
Examples of collective nouns. In English there is a group of nouns which despite their singular form they stand for collection. Below you can find a list of examples of such nouns.
- crowd
 - crew
 - family
 - jury
 - flock
 - team
 
These nouns can be used with verbs in plural and singular. In the last case we refer to the collection as a whole.
My family consists of 5 people. 
 
    My family are always quarrelling with one another.
The crew of this ship is too numerous. 
The crew were all wondering about the deck.