The crab bucket syndrom according to the urban dictionary:

"When a single crab is put into a lidless bucket, they surely can and will escape. However, when more than one share a bucket, none can get out. If one crab elevates themself above all, the others will grab this crab and drag'em back down to share the mutual fate of the rest of the group."
(https://www.urbandictionary.com/define.php?term=Crab+bucket )

When this syndrom is at work, the focus of team members is on saving oneself rather than cooperating to help the team.

As a coach, you need to adress this syndrom first. Its is a very complicated, not-at-all funny, problem so the temptation to sweep it under the carpet is probably great. But as long as this syndrom is at work, your coaching is weakened if not completely vain. Indeed, the group will tend to keep everything as it is and kill all changes.

Therefore

You need to understand what is happening in the team. Why are they in a crab bucket?

Are people feeling endangered? Is there a lack of trust? Why? Are there individual objectives and bonuses at work? Is there a conflict? Between 2 people? 2 groups? Are people feeling endangered by your coming?

Details

There is no perfect tool to deal with this situation. Every case will be specific. However, there are tools that can help you.

Tools for conflict

[WIP]

Tools for lack of trust

[WIP]