If your team name is a word which never meant anything officially and hasn't been used in a century, you're the New York Knickerbockers. People forgot what knickerbocker meant so long ago, that they just put another, similar, fake name on the logo and people just rolled with it.
So let's crack this like Geraldo cracked Al Capones safe. By that I mean the answer is about as interesting.
Apparently, in the 1600's, knickerbockers were a kind of rolled-up-pants --knickers-- the Dutch settlers wore. So similar to how you refer to that one guy as "short-shorts", people went ahead and called Dutch settlers "Knickerbockers". As you may remember from your history class, New York City was founded by Dutch settlers, and was originally called New Amsterdam.
As public fascination with Dutch settlers, and what-to-call-them wained, so did the name.
It was revived however, when literary legend Washington Irving wrote the satiric A History of New York from the Beginning of the World to the End of the Dutch Dynasty under the pseudonym Diedrich Knickerbocker. He used "knickerbocker" as a term to describe a New Yorker with Dutch roots.
As time went on, and meanings change as they do, the term eventually became used to describe anything New York and metropolitan.