Oops, it doesn't look like 'championships within a day' is a national day..

Other days

china

China Day
pumpkin

Pumpkin Day
latina equal pay

Latina Equal Pay Day
one

One Day
bow tie

Bow Tie Day
eat what you want

Eat What You Want Day
lisp

Lisp Day
boba

Boba Day
coffee

Coffee Day
stud

Stud Day