Why are they called CAPS? (International Soccer)

Factual Questions
1

In international soccer, an appearance for a national team is called a CAP.
Tony Meola just got his 100th “CAP”. Mia Hamm had 400+ “CAPs” (I think).
What does CAP stand for? Or are they caps, as in hats? Someone explain, please.

2

As in hats - teams of various sports used to give caps to members.

3

According to this, the term comes from headgear

4

Here is an article that indicates in Scottish rugby at least, physical caps are still given.