You buy it.

I don't know how you could explain it more clearly. Don't worry about the people who can't read.

Anyways, I think HBO has the fight. If that is the case then try PlayStation Vue. It's on AndroidTV and is a streaming cable service by Sony. No contracts and you can add HBO to it. After the month you can cancel.

You might be able to get it straight through the HBO app too. I used both a while ago, but forget if HBO Now or HBO Go is the stand alone app.

If you have a game system like Xbone or PS4, sometimes you can buy the fight on that.

A lot of people aren't really comprehending what you're asking and are just assuming you want an illegal stream. Which is fucking stupid, because you literally said "legally" in your title. Some people just can't fucking read I guess.

So I noticed that the fight (it's boxing, people... not UFC) is being sponsored by HBO, but I can't be sure that being an HBO customer and having access to their streaming app would also mean that you could watch PPV fights through the same app. I hope the PPV isn't restricted to people who haven't cut the cord, which I guess is the reason for this post.

Maybe /r/boxing would be able to get you a straight answer? I'm sure someone has legally streamed a previous PPV using some kind of app.

Slingtv says.... Maybe. https://m.facebook.com/sling/posts/2233526133540579

It'll be available through RingTV (Owned by GoldenBoy Promotions) so either hook up a laptop/desktop to your TV via HDMI or cast the tab through Chrome. Just a note RingTV stream uses different commentators than HBOs team.

You can't "legally" stream it unless you pay for it. Is this what you're asking?