Collective nouns (committee, team, squad, army, class, and the like) refer to groups. How do you choose a pronoun to refer to that committee, squad, or team? When the group is acting as a unit — doing the same thing at the same time — the noun is singular and the pronouns that refer to it are also singular. In this situation, the collective noun is paired with a singular verb also (if the collective noun is a subject).
Here’s an example:
The squad is on the move; it should be here in plenty of time for the battle.
The collective noun is squad. Because the whole squad is moving as a unit, squad pairs with the singular verb is and the singular pronoun it. Similarly, you need a singular possessive pronoun when the collective noun is acting as a unit, as in this sentence:
The cast will hold its annual Thank-God-Michael’s-Latest-Play-Is-Over Party tomorrow.
The whole cast is responsible for the party (although Lola is always complaining about doing all the work), so the singular possessive its works here.
Right about now you’re probably wondering what happens when the group isn’t acting as one unit. Simple. Just break the group down into its component parts and go for plural verbs and pronouns, as in this sentence:
Some members of the squad are eating pizza while others are oiling their rocket launchers.
Now you have a plural subject (members) partnering a plural verb (are) and a plural pronoun (their).
Sadly, there are a couple of complications in the collective noun situation. Read this sentence:
The audience rises and is ready to leave after a stirring performance of Michael's new play. (Actually, the audience was ready to leave after the first act, but Lulu had locked the doors.)
In the preceding example sentence, the subject, audience, is paired with singular verbs — rises, is, and was. Those verbs are correct because the audience acts together, a collection of people molded into one unit. So far, so good.
But if the audience is a unit, should the audience clap its hands or their hands? At first glance its seems appropriate, because its is singular, and audience is paired with singular verbs. However, the audience doesn’t own a big, collective hand. Every person in the audience has two individual hands. Body parts, no matter how unified the group, must belong to separate people. Therefore, you have to dump the collective noun and substitute members of the audience. Now you have this sentence:
The members of the audience rise to their feet and clap their hands.
Members is the subject. Because members is plural, so are the verbs and pronouns (rise, their) associated with it.
Here’s another sentence to figure out:
As the orchestra raises its/their instruments, Roger searches for the sheet music.
Orchestra is another collective noun. The verb is singular because the orchestra acts in unison, but its instruments sounds strange. Okay, maybe the orchestra owns all the tubas, violins, and other instruments of destruction. (You should hear them play.) So if the sentence were talking about ownership, its would fit:
The orchestra insures its instruments with Lloyds of Topeka.
However, the orchestra can’t raise a collectively owned instrument. Each musician raises his or her own. So their and musicians make more sense:
The musicians in the orchestra raise their instruments and prepare to demolish Beethoven.
To sum up the general rules on pronouns that refer to groups:
Collective nouns performing one action as a unit take singular verbs and pair with singular pronouns.
Possessive pronouns referring to collective nouns are singular if the item possessed belongs to the entire group.
If the members of the group are acting as individuals, drop the collective noun. Possessive pronouns referring to the members of the group are plural.
Body parts always belong to individuals, not to groups.