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Twitter (NYSE:TWTR) is quickly becoming the one-stop shop to stream sports online for free, after a series of recent deals with the National Football League, Major League Baseball, National Hockey League, and Pac-12. But as you might imagine, the social media company and its partners aren't giving online viewers access to every game and event. 

So here's a quick rundown of what sports you can watch online through Twitter, what the viewing restrictions are, and why Twitter is making such a big push into live sports.

Free football games

Twitter made its biggest move into live sports when it announced that it would pay $10 million to stream 10 NFL games for the 2016-2017 season. The games include the 10 Thursday Night Football games, which will be available on Twitter worldwide. 

Don't expect to find these games elsewhere online, either. The NFL said in a press release that Twitter is the exclusive over-the-top (OTT) streaming partner for the Thursday Night Football games. 

The good news for online viewers is that neither Twitter nor the NFL will require any type of login to watch the videos from the site, which means that nonregistered Twitter users will be able to stream the games as well. 

In addition to accessing live-streaming of the games, online users will also be able to view in-game highlights and pregame Periscope broadcasts.

Free baseball and hockey games

Twitter, MLB, and the NHL have yet to release the schedule for free online-streaming games, but the two sports leagues say they'll stream one game per week, to both logged-in and logged-out Twitter users.

The downside is that online users won't be able to watch nationally televised games or playoff games.

A Twitter press release said the baseball games will be available worldwide, with some international territory restrictions. 

The company also partnered with an OTT network, 120 Sports, to bring a new, exclusive nightly multisports highlights show to Twitter's platform, called The Rally. The company said it'll be the first-ever show of its kind to stream on Twitter. 

College sports streaming on Twitter

Twitter didn't forget about the college sports fans when its started partnering up for live games. The company is the premier streaming partner for Pac-12 Plus games and will stream 150 games in the 2016-2017 season from 12 universities. 

The games include soccer, volleyball, gymnastics, baseball, ice hockey, swimming and diving, softball, track and field, wrestling, lacrosse, tennis, and water polo -- notably leaving out football and basketball. There's no word yet on whether Twitter will eventually get these two college sports added to the list. 

But the games aren't exactly exclusive to Twitter. The university athletic websites and will also stream the games. 

Where are the NBA games?

The short answer? There won't be any NBA games streaming on Twitter. Sorry. Twitter did make a deal with the NBA, but it only includes two NBA shows made exclusively for Twitter. 

We don't know much about the shows yet, but we do know that they'll be weekly streams and that they'll air this coming season. 

The new partnership will also double the amount basketball highlights the NBA posts to Twitter's companies (like Vine), but it appears no live-streamed NBA games are in the cards any time soon for Twitter.  

Why this is good for Twitter

As its growth has slowed lately, Twitter is trying to find new ways to get its current users to spend more time on its platform, and attract new users at the same time. Streaming live games could help, but since the company's not requiring logins, it might not lead to many new users. 

But Twitter's main focus for streaming sports is the likelihood of bringing in additional ad revenue. Though Twitter is paying for the rights to stream the NFL games, it'll split revenue with the league from the ads it airs during the games. 

And the same goes for MLB and NHL games. Both of these leagues stream their games through the Major League Baseball Advanced Media (MLBAM) company, and Twitter has guaranteed MLBAM a certain amount of ad revenue from the partnership (though it hasn't said how much). After that requirement is met, the MLBAM and Twitter will split ad revenue. Twitter is also splitting ad revenue with the NBA for the weekly shows. 

The market for digital video advertising will hit $9.9 billion this year and reach $28 billion by 2020, according to Cowen and Company. Not all of that will come from live video, but Twitter sees the popularity of live sports as a way to tap into that vast advertising market. It's still unclear whether these streaming sports partnerships will pay off for the company, but investors should be pleased to see Twitter entering the massive sports market nonetheless. 

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.