Dave O'Brien believes he knows baseball: the rules of the game, trends in how the game has been played and managed during his broadcasting career, which statistics best show a player's real contributions, etc.
He certainly should know these things, since they are an essential part of his job. As the Red Sox's play-by-play announcer for NESN, he is the main guy in the booth. He should act as the conduit between the game and the fans watching at home. It's not asking too much to expect him to be more knowledgeable than the average fan on the street.