[Ref in PA]

If the other team has an immediate scoring chance, I would withold the whistle if I felt the injury was not serious. If the other team is setting up their offense, passing the ball around, walking the ball up the court, etc. blow the play dead and determine whether or not you want to beckon a coach/trainer on to the court.

As said above, if I felt the player was seriously injured or in danger of being injured further or in danger of injuring other players I would blow the play dead immediately.

In any event, as the trail I would stay with the player who is down until the play is blown dead per the guidelines above.