Deadspin has an excellent takedown of the “unwritten rules of baseball” by Dick Hayhurst, a former MLB pitcher:

I’ve heard all this stuff before, all throughout my playing days. Don’t run over the pitcher’s mound because it’s sacred ground. Don’t pimp home runs because it’s disrespectful to the game. Don’t throw inside unless you want one of your own players getting buzzed. Don’t do this or that unless you have enough service time under your belt, in which case do whatever you want.

None of the players passing along their wisdom seemed to realize that it was all completely arbitrary. No one came close to acknowledging, “You know, it’s stupid and none of us know where it came from, and before we go fracturing some poor rookie’s wrist because he looked too happy about going yard on a vet, we should really sit down and ask ourselves if the punishment fits the crime.”