Sorry to keep beating y'all down with my questions but I'm a novice to kilt wearing.

At many highland games and Scottish fests I've been to in Texas, Colorado and North Carolina, I've noticed what I perceive to be a casual look whereas the person is wearing a kilt, a kilt belt, some kind of T-shirt and sandals or tennis shoes.

The T-shirt is usually somewhat non-descriptive and doesn't necessary relate to any Scottish symbolism.

Would wearing a football jersey instead of a T-shirt with the casual kilt attire be out of line?