Well it is confusing because your examples are 100% wrong for US tax code.

Catching a baseball which might be worth $1M isn't a taxable event.
Painting a painting which someday might be sold at auction for $1M isn't a taxable event.
Digging up some shiny rocks that some culture someday may consider worth $1M isn't a taxable event.
Your house going up in value isn't a taxable event (for the purposes of income tax).

Selling the baseball, painting, gold, or your house ARE taxable events.