Despite declining TV ratings for National Football League (NFL) games, football remains the most popular sport among Americans. It's also a big industry, with the NFL generating estimated revenue of around $14 billion last season.

Another industry could soon eclipse the NFL, though, if projections from research companies Arcview Market Research and GreenWave Advisors are on target. Both Arcview and GreenWave think that the marijuana industry will be bigger than the NFL by 2020. Could this really happen -- and, if so, what are the best stocks for investors to profit from the trend?

A football with players in the background

Image source: Getty Images.

No Hail Mary passes needed

Arcview estimates that the U.S. marijuana market generated revenue of $6.7 billion in 2016. That's roughly half of what the NFL made, so there's a long way to go for the marijuana industry to even catch up with where the NFL is now. And that won't be enough.

In 2010, NFL commissioner Roger Goodell announced a revenue target of $25 billion by 2027. To attain this goal, the NFL would probably need to pull in revenue of around $18 billion by 2020 to be on track.

Can the U.S. marijuana industry's revenue realistically top $18 billion within the next three and half years? Maybe. Arcview's data showed that the industry increased revenue last year by 30%. If that same level of growth were achieved over the next few years, the U.S. marijuana industry would make a little over $19 billion by 2020 -- ahead of where the NFL needs to be to stay on pace for its revenue goal.

This annual growth rate could even be pessimistic. California's legalization of recreational marijuana opens up a huge new market. Cowen and Company thinks that the California market alone could enable total U.S. marijuana revenue to soar to $50 billion by 2026.

What about the Trump factor?

There's one thing that could derail growth for the booming marijuana industry, however: the Trump Administration. There was some good news for marijuana proponents in the omnibus spending bill passed by Congress and signed into law by President Trump. No money was provided for the Department of Justice (DOJ) to go after states that have legalized medical marijuana.

This spending bill was a temporary one, though; it only funds the federal government through Sept. 30, 2017. Also, it only prevents the DOJ from going after states that have medical-marijuana laws. States like California and Colorado that allow legal use of recreational marijuana are fair game.

In February, White House spokesman Sean Spicer warned that there could be greater enforcement of federal laws prohibiting the sale and use of marijuana. Attorney General Jeff Sessions has been a vocal opponent of marijuana legalization.

On the other hand, Sessions reportedly gave Colorado's Gov. John Hickenlooper reason to believe that a federal crackdown on legalized marijuana isn't on the way. There's also probably a good chance that Congress will insert similar language, prohibiting the DOJ using money to target states legalizing medical marijuana, in any future budget legislation.

Marijuana growing in green house

Image source: Getty Images.

Super Bowl stock

There are several promising marijuana stocks that are biotechs. A few others focus on the Canadian marijuana market. However, most of the stocks poised to benefit from growth in the U.S. marijuana market are very small. It's difficult to predict which of these small players will succeed, fail, or be acquired along the way.

Medical Marijuana, Inc. (MJNA 15.00%) stands out as one of the few U.S. marijuana stocks that has a reasonably large market cap and could experience tremendous growth as the size of the marijuana industry increases. The company markets a variety of cannabis products, including its cannabidiol branded as Real Scientific Hemp Oil.

Over the last 12 months, Medical Marijuana stock has soared more than 130%. However, that impressive performance masks more recent problems: Its share price is down close to 50% so far in 2017.

I think that the safest marijuana stock bet is Scotts Miracle-Gro (SMG 0.86%) The company stands to benefit regardless of which individual marijuana growers come out on top. Scotts sells nutrients, supplements, lighting systems, and other supplies that are critical for growing marijuana, and has steadily increased its presence in the market to supply marijuana cultivators in recent years. Investors should like that Scotts Miracle-Gro is already quite profitable, and even pays a nice dividend currently yielding 2.3%.

The U.S. marijuana industry probably will become bigger than the NFL in the next few years -- if not by 2020, then soon thereafter. Assuming that happens, the most likely stock to be the marijuana equivalent of a Super Bowl winner could very well be Scotts Miracle-Gro.