Comment by VWWHFSfQ
It's this company [1].
They pay people to watch every play of every game and apply a formula that grades the relative difficulty in order to develop their advanced statistical models.
Some of this stuff has been automated, but a lot still hasn't and still relies on the "eye test".
Thats one of several companies.
I would be curious to see how automated this stuff is now with computer vision but I doubt its mostly automated.