I agree with post 4 that you need to narrow your topic before you start writing. The first step isn't necessarily writing the first sentence of the introduction. Usually, the first step to writing an essay is writing your thesis statement. Only then can you begin to write the paper itself. Your first sentence should be something that draws the reader in but it should also point in the direction of your thesis. For instance, you might make a concession statement where you acknowledge the opposite viewpoint. You might make a comment that confirms your stance on the topic. Or, you might start your paper with a far more general comment such as "sports are an ancient rite of passage."
First, you need to narrow your topic quite abit. What you have posted is too broad. Let's be more specific. Suppose you were to write about sports in high school. Now pick a side. Let's go against the trend and argue that sports are a negative for high school students in some way. A good thesis statement (in my opinion) coud be something like:
Although high school sports have been extremely popular for decades, they often negatively affect the athletes in ways that are rarely acknowledged.
Now you would spend the body of your essay giving support to this idea.
Considering the depth and breadth of the subject pointed out in the post above, you might want to craft a thesis that attempts to speak to that complexity.
Sports have been around for a long, long time. They serve as exercise, entertainment, therapy, community glue (bringing people together), and even industry (they make money).
Are you talking about sports for individuals (why it's good for us to participate in sports) or are you talking about spectator sports (why it's good/bad for us to have massively popular spectator sports)? On the good side of each: For the first, you could talk about the benefits in terms of fitness and self-confidence. For the second, you could talk about entertainment and a feeling of kinship with other fans.