Bang! A beautiful cross and a header into the top corner of the net -- it's the sort of moment that's perfect for World Cup fans to share on social media. Until, that is, the video disappears.

As the Wall Street Journal reported Monday, ESPN(S dis) and Univision have been sending in copyright strikers to take down videos of World Cup goals. In response, sports site SB Nation has had two social media accounts suspended, while Slate had to remove a popular clip that showed 138 goals in short succession.

One popular target for ESPN is Vine, the Twitter-owned(s twtr) service that lets users take looping six-second videos on their phones and quickly share them on social media or websites. To show how easy it is, I've embedded a Vine I made while watching a random piece of action from the Argentina-Switzerland game (sorry about the final outcome, Swiss fans):

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Fortunately, it is not every World Cup clip that ESPN, which is working with FIFA to enforce copyright, finds objectionable. According to the Journal, it is goal highlights -- rather than things like fan celebrations -- that are attracting the takedown notices.

All this, though, begs the question: does ESPN have the right to remove short goal videos at all? Under the doctrine of fair use, people can display a copyrighted work without permission in certain circumstances. For instance, an appeals court in California last year said that the musical "Jersey Boys" was allowed under fair use to play a 6-second clip of the Ed Sullivan show. And, indeed, the history of fair use and hip-hop explains why Vine videos are six seconds in the first place. There's even a website devote to Vine videos of TV's best moments.

In the case of the World Cup, however, the law is not so cut and dried. That's because fair use is not determined by a bright line rule, but by a four-part test that looks at things like the purpose of the use, and its effect on the market value of the original work. ESPN executives, who paid $100 million for the rights to the 2010 and 2014 broadcasts, would no doubt be quick to claim that goal highlights are the most valuable, important moment of a game -- and that fair use should not apply. They are also no doubt keen to protect their current partnerships with Google(s goog) and others to distribute the highlights on their own terms.

But while the legal status of goal highlights is unclear, many other World Cup related clips clearly are fair use. The problem right now is that it is ESPN who gets to decide what is fair use and what is not. Under the rules of copyright law, ESPN lawyers can shoot first and ask questions later; it's true that people can challenge the takedowns as invalid, but that process takes at least 10 days, by which time the excitement of the moment is long past.

Under these circumstances, the best outcome may be for Twitter and other companies that host such clips to challenge the takedown notices, but so far they appear unwilling to rock the boat.

So for now, the best fans can hope for is that ESPN and FIFA will have the sense not to go overboard, and use copyright to kill the social media excitement that has become part of this year's tournament. And, if you've had a World Cup highlight takedown, please leave us a comment if you think that was fair, and what you think the rules should be.