Deductive reasoning contains three basic parts: a major premise, a minor premise, and a conclusion (the formal version of this is a syllogism). So, if you are writing about two sports, your major premise in the paragraph should be a broad, widely accepted statement about sports that relates loosely to your argument. For example, you could discuss the rise of sports in the world; it just needs to be a statement that someone who favors Sport A or someone who favors Sport B would agree with.
Next, you need to include evidence which will lead to your conclusion (a statement which identifies which sport is better and why). The evidence could feature statistics which show that Sport A has more health benefits than Sport B or which demonstrate that more people watch Sport A than Sport B. Whatever your evidence is, it needs to be factual, and it needs to lead your audience naturally to your conclusion.
Finally, near the end of your paragraph, you should include a clear statement that identifies Sport A as the better sport--this is your "conclusion," and it should be obvious to your reader that you have "deduced" this conclusion from your major premise and evidence. Good luck!