A Robust Definition of a Sport

In doing some reading in another context, I came across the following minimum criteria for something to be a sport:

“An activity is not a sport unless there are challenges to be overcome and a clear set of rules about how to confront these challenges.” -- J P Spiro (2008) Defending the Master Race: Conservation, Eugenics, and the Legacy of Madison

This was offered as a way to distinguish a "sportsman" from a "market hunter" in the US in the late 1800s. But it got me to wondering if it has a more general application. Clearly, the two criteria--challenges and clear rules--are not sufficient to define a sport, but are they necessary?

I am sure that ground has been broken on the question of what makes a sport a sport, so pointers to that literature would be greatly appreciated.