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I think they are wearing it for the passing of Red Auerbach, one of the winningest coaches in NBA history.

Yeah, when a NBA great dies, a player from a particular team, or someone having a lot to do with an organization dies, then they wear the lack stripe on their jerseys.

It is usually some black tape placed on their uniform and it is usually worn when a player or former great has passed away. The Celtics earlier this year did it for Dennis Johnson. It's a mark of respect for all those who have gone before you in that uniform!

yes or someone part of the team that was very important so they wear that as respect.