The NBA offseason is officially off and running, and the Boston Celtics have taken center stage. One day after agreeing to trade Jrue Holiday to the Portland Trail Blazers, the Celtics have reportedly come to terms on a three-team deal that will ship Kristaps Porziņģis to the Atlanta Hawks.

The Boston Celtics traded Jrue Holiday and Kristaps Porzingis. Why did they do that? What could be next? Here's an explainer.

The Celtics shipped the 35-year-old Holiday to the Portland Trail Blazers for the much-younger Anfernee Simons, and Holiday wasn't a fan of the move. Per Heavy Sports' Steve Bulpett, one source said Holiday is "pissed" about being traded to Portland.