I'd like to start off by saying I fundamentally believe in Peter Lynch's tenets of investing. "Invest in what you know" is a wise way to invest -- if done properly. When I walk down the street, I find myself noting what people are wearing, what pipes are going into buildings, what new stores are coming and in what areas. More than financial statements, talking heads on CNBC, and even my own field of finance writing, the average investor can benefit the most from simply observing the surrounding world.

Caveat emptor: Observing is one thing, but if you live and breathe the product, your Lynch-ian vision may be fogged.

Ole, ole ole ole!
As of Friday, one of the best-known and most valuable sports franchises in the world is a U.S. publicly traded entity -- Manchester United (NYSE: MANU). Though we 'Mericans historically have little interest in the game, it is nonetheless the biggest sport on Earth. Take a trip to South America, Europe, Africa, or Asia, and you will see diehard fans that put your average NFL enthusiast to shame.

While each nation and the cities within are feverishly loyal to their respective teams, some franchises have transcended all borders to become international favorites. Manchester United, or Man U for short, is one of those teams.

Man U employs some of the biggest names in the game and has historically been a repeat powerhouse -- though lately it's fallen on tough times. The team was purchased in 2005 by American billionaire Malcolm Glazer for around $1.5 billion. At today's implied valuation from the IPO, the team is worth more than $2 billion -- one of the top five most valuable sports teams in the world.

If you are a soccer, er ... football fan, you may think you're being a Lynch-investor by jumping in on this seemingly obvious "buy what you know" opportunity. Now, this is not because I happen to be a Barcelona supporter, although I am, but I believe this is one common brand you are wise to pass on.

Management yellow card
For one thing, in the prospectus for the Man U IPO, one will read that Malcolm Glazer and family will hold super-special shares that ensure they retain control of the team. So just because you buy the stock doesn't mean you can start throwing suggestions in for new player acquisitions.

Also, upon his initial purchase of the team, Glazer saddled the organization with hundreds of millions in debt -- a typical leveraged buyout practice. Analysts and fans believe this fact has held the team back from its full potential as a global sports powerhouse.

Other recent IPOs with similar management practices: Facebook (Nasdaq: FB) and Zynga (NYSE: ZNGA). I have several issues with these companies as investments beyond the fact that their senior executives/founders have special voting privileges that should never exist in a public company, but that is certainly a big part of it. Since its IPO, Facebook has gone from $38 per share to a bit over $21. Zynga is trading around its 52-week low -- which represents the vast majority of the value of this company gone in a year. Again, it's not solely because of special management shares -- but if I am invested in a company that's tanking, I would like to have a voice at the annual meeting. Investors in Facebook, Zynga, and now Manchester United will have no such luxury.

Practice your fundamentals
The business managers should be on the field with the players jumping through tires and doing calisthenics. The financials have been undesirable, and in the prospectus, the company forecasts lower revenue in the coming year. When I have taken too many crazy pills and begin to think about investing in IPOs, I still shy away from those that are making their market debuts with negative guidance. I can't quite put my foot on it, but something seems off.

If you have to invest in sports ...
There are several great investments for the sports enthusiast. Just look at Nike (NYSE: NKE). The sportswear behemoth brought in $3 billion more in revenue year over year to $24 billion in 2011. Its footwear segment saw 17% growth. For a $43 billion company, near 20% growth is utterly phenomenal.

The company is represented in nearly every major sport and inks deals with top organizations around the world. If you want to buy what you know in the sporting world and still see positive returns, you'll look here first.

Our analysts here at the Fool have gone into more detail about the aforementioned Facebook and Zynga stories. I find the businesses to be particularly unattractive, but take a look for yourself and see what challenges and opportunities lie ahead for both Facebook and Zynga inside our brand new premium reports.