I think you miss the point. If you have to start arguing what is and isn't a substantial effort then you're probably going to fall foul. This is an open source

I think you miss the point. If you have to start arguing what is and isn't a substantial effort then you're probably going to fall foul. This is an open source schema for storing data, why not re-acquire the data from a fresh source and make that open source too? This avoids pulling it from an existing and potentially protected source. You could have members of the public individually enter historical scores, and each one provide proof of the score (e.g. a photo of a result in a newspaper or a photo of the matchday guide). You could verify correctness of that acquired data by comparing to a few known data sources (even if they were protected). So long as you were close enough in fact to not alter history it was probably right, and correctable in the future (editable like a wiki). If you use one of the existing datasources you'll find yourself with a lawsuit if you reach any reasonable size.