Do you have access to see if it will work on another device (ipad or phone app)?
Have you looked at your browser settings - Websites, and also Privacy? They would want to see your general location, not using a private browser setting. You might have to experinent with the settings, refresh the browser (dump the history each time), and see what works. It could be your defaults are too restrictive. I have a couple of trusted websites that won't work unless I open up to allow them a few things.
1) Suggest turning off "Content Blockers" to start. That seems to be one that resolves many problems I've encountered. YOu can make it specific to just the NBA site. Open up the NBA page that doesn't work, and then open up Safari>Settings. Click on the Websites tab. From then on left look for Content Blocker and on right the default is usually to not allow.
2) Next, in same Safari Settings window, scroll down on left frame to "pop up windows". NBA sounds like it would love to give you lots of goodies for you to see in addition to the content you watch, so it may require you to Allow popups. Again, this is just for that website.
3) Next go to a different tab in Safari Settings > Privacy. Try each of these one at a time...
-Uncheck Cross site tracking. that's a common hang up when a site runs ads or has a lot of streaming content.
-next, toggle the Hide IP Address from the default, to "Trackers only".
You easily switch all this back later on if you choose.
