The MLB takes the enforcement of pine tar rules in baseball seriously. The league has a number of measures in place to ensure that players are not using illegal substances to gain an unfair advantage.
One of the primary ways that the MLB enforces the rules is through umpires. Umpires are responsible for checking the bats of all players before each game. This is done to ensure they don't have too much pine tar or any other illegal substances on them. If an umpire deems a bat illegal, they will remove it from the game and the player will be ejected.
In addition to checking bats, umpires will also monitor pitchers for illegal substances. If they find an illegal substance, the pitcher will be ejected from the game. They may face additional penalties, (see Max Scherzer).
Players who are found to be using illegal substances may also face fines and suspensions from the league. The severity of the punishment will depend on the nature of the offense and the player's history of rule violations.
Overall, MLB maintains a level playing field by actively enforcing the rules concerning pine tar and other illegal substances. Despite having turned a blind eye to the steroid era in the 90s, MLB is now actively addressing the issue and striving to ensure that all players play by the same rules.