Teammates stop passing to the kid who never passes back. Trust on the court runs on the same rules as trust anywhere.

Cooperation is maintained by a rough sense of reciprocity that nobody states out loud. People notice, without keeping a formal tally, whether their effort comes back, and when it consistently does not they simply stop directing anything your way. Nothing gets announced; the opportunities just stop arriving.

Look at where you have been receiving without returning, in a team, a group project, a friendship. Send something back this week, unprompted, in whatever form fits. The flow reopens much faster than you would expect, because most people are not keeping a grudge, only an honest impression.