The Baseball Codes is all about those "unwritten rules" you hear about if you watch or listen to sports and sports-related discussion. When is it OK to throw at a batter, what methods for stealing signs are acceptable, things like that. My dad gave the book to me, and it has some entertainment value in the stories and anecdotes that Turbow (and Michael Duca) have filled the book with. Some of them I remember, some are before my time.
As for the actual discussion of these codes, that was less interesting because it becomes abundantly clear that players, managers, sportwriters, and fans simply skew the rules to be whatever they need to excuse their actions, while condemning those of the opponent. I mean, people can't agree on whether so-and-so was right to throw at that other guy, or if Ben Davis was right to bunt for a hit and break up Curt Schilling's no-hitter. I say he was, because it was a 2-0 game, so with him on base, the tying run was at the plate. Absolutely nothing wrong with that. So it all comes off as a bit silly, even for something dealing with a game.
There's also a rather tedious bit at the end where they discuss the deterioration of the Code, which sounds a lot like nostalgic "players today play for money, they don't care about the game like the old-timers do" bullcrap I can do without. So I'd advise giving it a readthrough for the stories alone. Just skip the last chapter and you'll be fine.