Facebook (FB) announced on Wednesday night a new feature, Facebook Sports Stadium, and called it "a place devoted to sports so you can get the feeling you’re watching the game with your friends even when you aren’t together." But that place already exists: It's called Twitter.

Sports Stadium is a competitive shot across Twitter's bow—specifically, it targets what Twitter (TWTR) users and journalists call "Sports Twitter," the subset of the platform that goes nuts during exciting sports events, when people are so confident that everyone is watching the same event that they often use mere shorthand, minus context, to react to a play. For many sports fans, Twitter is the platform they rely on for real-time, instant commentary and analysis about games as they watch, checking to see what former NFL referee Mike Pereira has to say about an iffy call, or, say, if LeBron James will comment on another player's trash-talk.

Now Facebook wants to be that platform. And even if some might say that sports fans who love Twitter are already groomed to issue their thoughts in 140-character bursts, Facebook has an instant competitive advantage simply because of its size. Much like when the NFL released a mobile video platform last season, NFL Now, Facebook is big enough that a built-in chunk of people will at least try any new feature no matter what. Facebook has 1.5 billion monthly active users, and says more than 600 million of them self-identify as sports fans; Twitter has somewhere north of 300 million. The new feature makes sense in another way: Facebook knows which sports teams you root for (whether you like it or not) and has already been nudging users to post a status update when their team is playing.

Lots of players on the field

But Facebook isn't just competing with Twitter here. It's also jumping into a crowded playing field of myriad other apps and features for real-time sports chatter. Almost every one of these new entrants has some kind of involvement from a pro or former pro athlete.

Take GameOn, which re-launched in August and combines elements of Twitter, WhatsApp, and ESPN's mobile score-updates app. The company hopes to become the go-to place for fans to discuss sports, and recently added an "athlete portal" as well. (Sound like anything else that was just announced?) NFL alums Joe Montana and Lawyer Milloy are both investors. Or take Thuzio, the app from former New York Giants star Tiki Barber that initially allowed sports fans to pony up a fee for an athlete to come watch a game with them or connect over FaceTime. (Thuzio has since pivoted to a B2B model that connects brands to celebrities for hire.) Or take Crowd Cam, launched two years ago by former NFL guard Mike Wahle, which aimed to cull all of an athlete’s or a team’s social media presences on one page to allow fans to chat and connect with them. Even a company like Whistle Sports, a digital video network that scored exclusive partnerships with a number of athletes who have devoted followings, is touching this space.

And those are just the upstarts. Bigger, more established social media platforms have also been going after sports fans. Most notably, Snapchat's "Discover" tab now shows live "stories" from every NFL game that cobble together videos submitted by fans who are at the games. Periscope, similarly, lets fans stream live video from a sports event, and fans do it even when they've been told not to, like when Floyd Mayweather fought Manny Pacquiao last year and some attendees took to Periscope to show the fight. Meanwhile, the NFL, Major League Baseball, and other sports leagues and teams rely heavily on Instagram these days (which is Facebook-owned) to post instant score updates or behind-the-scenes videos of players.

Getting real-time

So: How scared should Twitter be of Facebook Sports Stadium? One social marketing executive, who did not want to be named because he works closely with both companies, says the new feature is no automatic score for the social network. "Facebook isn't really a real-time app, I don't really think about going onto Facebook and posting live updates," he says. "Faceook is trying to create an artificial-use case, that's one big problem. That hasn't happened on Facebook up until this point, and they're trying to make it happen." Expect more Facebook products that target real-time data soon—the company is going after Twitter's specific niche. And it is doing this at a time when Twitter has been slammed for its struggle to make more money. Investors have clearly paid attention to this issue: Facebook shares are up 21% in the last year; Twitter is down more than 54%.

"I don't think Twitter is nervous about Facebook specifically," this executive says, "but they are nervous about all the different platforms encroaching on real-time data, because Twitter is the real-time platform, whereas everything else is not."

Or at least, others are not supposed to be. But Facebook and Snapchat refuse to play nice and stay in their box. Twitter will have to reckon with that competition more and more.