superstars survive on and value their reputation above all else, you can use that to motivate. Review with the team how productivity is measured and the goals the team is striving for. Then, call out someone on the team by name who is doing the most to get the team where it needs to be and give them a reward. It doesn't matter what the reward is, a random sticker will work just fine. Your superstar will see the writing on the wall and step it up so they get the callout and reward next time.

I've seen this at work with a Managing Director and her direct reports. Direct reports to a Managing Director are hyper competitive and cutthroat. Think of them like the velociraptors in Jurassic World, if you can keep them focused and not killing each other or everyone around them they're a very powerful force. This MD would just hand out verbal "gold stars" on an all hands call. The DRs would get noticeably upset when they did not get the "gold star".