I've wondered that. At concerts and other events the small print usually says (paraphrasing): "No professional photography or video footage may be taken unless prior authorisation has been granted". You can get HD cameras no bigger than LEDs these days, so it is an intriguing question.
Besides, where do you draw the line between filming a two-minute clip of a penalty being scored and five minutes of open play? Extend that to 15 minutes and where does that leave you legally? If you disseminate the footage for "educational or personal purposes", does that get you out of trouble? What about the resolution and audio quality, does that matter?