There are various routes into teaching but they all involve acquiring a university degree. Some good GCSE results, including Maths and English are a starting point. Then some fairly good A-level results (possibly including a subject such as Human Biology) are required. The usual route after that is a 3-year university course in Sports Science (or a related subject), followed by a year's teacher training.
See here:
http://www.tda.gov.uk/Recruit.aspx
and here:
http://www.learndirect-advice.co.uk/helpwithyo urcareer/jobprofiles/profiles/profile1105/
Chris
PS: All of that assumes that you're in the UK. Your use of the word 'major' [which isn't used in UK universities] suggests that you might be somewhere else in the world - or just that you've been watching too many American TV programmes ;-)
If you're not in the UK, either post on a message board based in your own country or post again here (stating where you're based) and someone will try to track down the information for you.