Whistle! is based on a popular manga under the same title published on weekly “Shounen Jump” by Higuchi Daisuke. It was made into anime to celebrate 2002 FIFA World Cup which will be co-hosted by Japan and Korea. The story focuses on Kazamatsuri Sho, one of the best junior high school soccer player. The theme of the anime is youth, friendship, a hero who try hard without giving up his dream to be the best soccer player and his team mates.
Descriptions taken from AniDB.net