Donatus Cannot participate in sport leagues on account of the unfair advantages their students posses.
Not only this, but magical users or nonhumans even in other schools are barred from sports participation outside of nonserious clubs

Salem said:

Elena wouldn't care much about that, she isn't a sports person but does that include super tame sports? Or sports with little competition? Like.. kayaking? Fishing, Skateboarding?

It includes any sorts of competitions, tournaments, conferences, leagues, etc.
For example, one could argue a fae would have an unfair advantage at fishing due to heightened senses or a stronger connection to nature, so any competition against them is immediately skewed.

Recreational sports are a-okay though

It's one of those very unfair laws that has stayed firmed