Were/was, quick help needed

[potplant]

Could someone tell me whether I should use were or was in the sentence below:

One of our client's teams were listening

(and is the apostrophe correct?)

Was. One of the teams was listening. Two of the teams were listening.

If you are only talking about one client then the apostrophe is correct.

Thanks.

For the apostrophe the team belongs to one particular client but there are lots of clients. So it's correct?

The apostrophe would normally be correct only if you have just one client. "our client's teams" is an entity in itself, and it is only meaningful if you have just one team, or if you have already referred to the one client you're talking about; otherwise it's a grammatical mistake. If you have several, and you haven't already identified one, it should be "our clients' teams", and then the "one of" specifies one of them, without you specifying which client or team.

I meant to say "is only meaningful if you have just one client", of course...

[One of our clients] (had) a team (that) was listening = one of our clients' teams was listening.

One of our (many) clients (but we're only talking about one client here), who has has many teams (but we're only talking about one specific team belonging to one specific client), had a team that was listening = one of our client's teams was listening.