It's usually a member of the print media.
The Official Score Keeper.
The answer depends on what statistics you are studying: scores, games won, or whatever.
The box scores of baseball games published in newspapers of 1884 had no room for such a long name. Therefore the nickname of Connie Mack saved space both in box scores and write ups on baseball games.
One can find the latest scores of sports games by watching the sports games, by reading tweets in response to the sports games or by watching the news where they will often announce the scores.
A big board in baseball is where their win scores are.
World Series scores for past games can be found from many different resources. The most reliable resource is the official MLB website, which archives all past scores and records.
You just play games and submit your scores.