Hashtags are a great function which allows Twitter users to tag tweets to give more context to them. Hashtags can also be used as a way to designate the tweet to particular conversation or chat. In sports, many commentators use hashtags as way to get people who are watching the telecast to ask them questions. For example, if the commentators name is Jack, Twitter users who are viewing the match can tweet questions to Jack by adding a hashtag such as #AskJack in their tweet.
Via Brian Yanish - MarketingHits.com