Hi All,
I have the same issue. :-(
I found a solution though! :-)
Firstly, find the sports calendar you need via a google search. Usually a .ics file.
I found my football team via fixture.es. They have loads of leagues and competitions across the world, from the EPL to the MLS. (Btw I'm in the UK.)
For my NFL team I had to look a little harder. I found the file/url option deep in the team's website.
Secondly, open Outlook in your browser. This is important, it will not work from within the Outlook app. (That's my experience.)
Open your calendar, then click on 'Add calendar'.
In the box that opens click on 'Subscribe from web'. (Screenshot below.)
Copy paste the file / web address from your google search.

Then click on 'Import'. From memory it took a few seconds and then there was a confirmation.
Next, go to the calendar menu on the left and double check that this new calendar is selected/ticked.
You should see the games in your calendar. (You can then select the colour you want, to differentiate it from your other calendars etc.)
As a final check, I went to my Outlook app and checked the new calendar was there (it was). I had to select/tick it in the Outlook app, and then the games appeared! :-)
I hope this helps everyone.
John