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If we are playing catan and the robber is on an 8 and an 8 is rolled, but someone plays a knight card and the robber is moved..... Can that player then collect resources because the 8 was opened on the same turn and is no longer blocked?
By the time you roll, it's too late. You can play the card before rolling, in order to move the robber and hope for the best. But when you roll the die, you immediately dole out the appropriate resources, so if the robber is still there, you don't get anything.