I agree that having specific tags such as london-2012 is good for the site, but not at the current time. We don't have enough users that use them, so maintaining such user-friendly tags would be an overkill; specially because they will probably not be used a few weeks after the event is over.
So I'm proposing the idea of having tags for years, and use them with the sporting event required. For example if we add 2014 to our tags, then it could be used with the other ones that already exist to address questions regarding 2014world-cupor 2014olympicsor 2014nbaor 2014tour-de-france... . This way we don't need to make or keep tags that won't be used after the event is finished, and if someone happens to have a question about a tournament/competition in the past, they can use the year-tag as well as the name of the tournament/competition.