The Second Negative Constructive (2NR) and First Negative Rebuttal (1NR) are given by different people and are different lengths (2NC, 8 minutes; 1NR, 5 minutes), but the speeches function in similar ways. Collectively, the two speeches are the “negative block,” and both speakers have similar responsibilities.
What the two speakers share in common is the job of defending the negative arguments that were first advanced in the 1NC.
So, imagine that the Negative presented a topicality argument and a federalism disadvantage in the 1NC. They may also have made some other arguments on the case. In the negative block the 2NC, for example, would answer the 2AC arguments against the federalism disadvantage and explain why the negative should win on the federalism disadvantage. In the 1NR, the speaker would extend the arguments the 1NC made against the advantages and solvency and then answer any 2AC responses to those arguments.