The unwritten rules include:
For the batter
Do not bunt to break up a no-hitter
Do not swing on a 3–0 count when your team is ahead
Do not spend your time admiring a home run you hit
Do not steal bases if your team is ahead by a significant amount
Do not swing at the first pitch of the at-bat if the pitcher has allowed back-to-back home runs
Do not work the count if your team is winning or losing by a significant amount
Do not rub the spot where you were hit by a pitch
Do not walk in front of a catcher or umpire when walking to the batter's box
Do not stand on the dirt near home plate when the pitcher is warming up
Do not assist a member of the opposing team
Do not speak to a pitcher who is in the process of throwing a no-hitter
For the pitcher
A pitcher who is removed from the game in the middle of an inning must stay in the dugout until the end of the inning
A pitcher should not indicate displeasure if one of his fielders commits an error