TYPICAL ERROR The home team was already on the field. They were warming up for the big match.
CORRECTION The home team were already on the field. They were warming up for the big match.
EXPLANATION Collective nouns describe groups, as in team, crowd, jury, audience and committee. Such nouns can be regarded as either singular (e.g. The team was ...) or plural (e.g. The team were ...), depending on whether we are thinking of the group as a single body or as a collection of a lot of individuals.
How we treat collective nouns depends on the context. In the typical error above, the team is a set of individuals warming up so it is best to make all the verbs plural.
Once the usage has been decided, it needs to be consistent. Don't say The team was in one sentence and then in the next say They were (as happens in the sample typical error above).