English Grammar: Agreement of Pronouns

Agreement — Pronoun with Collective Nouns

Collective nouns are singular when they designate a group acting as a unit. They are plural when the members who make up the group are acting independently. The pronoun that takes the place of the collective noun must agree with it in number. If the collective noun expresses a singular idea, the pronoun is singular. If the collective noun expresses a plural idea, the pronoun is plural.

The band played its fifth concert. (acting as a unit)span

The band were tuning up their instruments. (as individuals)span

You can easily see that the second sentence could not refer to the band as a unit. That would mean that the members of the band were all working on the same instrument.