The MLB will now require all teams to “muddy” their baseballs, pre-game, in the exact same way. Gianmarco Castronovo discusses the technique that teams must follow:

Teams in the MLB will have to add a new step to their before-game rituals, according to an official memo.  Muddying is the process of removing gloss from the surface area of a baseball.  This effectively gives pitchers a better grip on the ball.  It’s also nothing new, as teams in the MLB have been doing it for decades (as Gianmarco Castronovo recently discussed on his Medium blog).  What is new is that now, teams no longer have options when it comes to “how” they muddy their brand new baseballs.

The new league-regulated technique for muddying requires clubhouse attendants to prepare each ball by rubbing it in Delaware River mud.  This is to be performed before each and every game and in no other way than by following this specific routine.