One thing I would do if I were writing about a sporting event would be get a local newspaper, or get online and read some actual stories on prep sports. You can get a feel for how descriptive essays on sports are written.
Another suggestion is to make sure you have a strong introduction. Several supporting paragraphs and a strong conclusion. Use vivid adjectives to describe the tournament and the individual games.
If you are describing one specific game you might say something like:
"Tigers stomp the Rams on the way to our exciting regional finals. The match was intense and suspensful right up to the last set of the match. The teams were tied at one set each and the final set was tied. As John stepped up to the service line the noise from the fans was defening....."
You need to be sure to tell all the who, what, where, when, and how's in your essay and you need to make the game come alive in your story. There are some discriptive links below.