Definition
A rebuttal is a response that engages a specific argument your opponent actually made, rather than a restatement of your own case. A real rebuttal shows the judge three things: that you understood the opponent's argument, that a specific part of it is weak, and why that weakness matters to the outcome of the round.
Example
Opponent's argument: "Raising the minimum wage will cause job losses, studies from other regions confirm this." A weak rebuttal just says "no it won't." A real rebuttal engages the mechanism: "those studies come from regions with very different labor markets, and more recent research in comparable economies found no significant job loss at similar wage levels, so the evidence for that mechanism is weaker than presented."
Common mistakes
The most common failure is delivering a second speech instead of a rebuttal: repeating your own arguments, louder, without ever referencing what the opponent said. Judges notice this immediately, because nothing in that speech shows engagement with the actual disagreement in the room. Always anchor your rebuttal to a specific sentence or claim your opponent made, not a stronger or weaker version you constructed to be easier to answer.