When searching for Athletes in any part of Portal the search functionality is the same. It searches both First and Last Name as the search term, and treats a space as an 'Or'.
Searching "John Doe" would search for John in all names, or Doe in all names. If an Athlete has either John or Doe in their first or last name it's considered a match.
Therefore, if the Athletes list is:
Then searching for “John” would return “John Doe” and “Jamie Johnson”. Searching for “John Doe” would return all three, because all three have either “John” or “Doe” in their name.