A Sports Uniform is Made by Adding Numbers

In order to make a uniform, you must add numbers to a piece of clothing to identify a player from another player. The word uniform is derived from the Latin word uni- which means to bring together to make one. It is also a Latin prefix that means one.

Unies - A collection of Numbers

All professional sports teams have a unique uniform. These uniforms separate one team from another team. Also, with the numbers printed on each uniform they separate one player from another.

ESPN commonly refers to a teams unies. There is a simple connection between naming the decade the Unies and a team's unies. They both have numbers in common.

The numbers to make up a uniform are the numbers between 0 & 9. The numbers in this decade are 0 & 9. So unies works for both terms.