After the recent controversy over foreign substances in MLB, the league has really tightened the rules. Now, pitchers can't have anything on them when they come to the mound, and umpires are doing regular checks. If they find anything suspicious, the pitcher gets ejected right away.
To further control the situation, MLB introduced new regulations, including placing humidors in all 30 ballparks to keep the baseballs' moisture levels consistent. This helps ensure the balls behave the same, no matter where the game is played.
On top of that, teams can no longer choose their own rosin suppliers. Before, they could buy from any company, and there wasn't much oversight. Now, MLB has partnered with Pelican Bat Wax, a small company out of San Francisco, to be the league’s exclusive supplier for rosin bags. While some pitchers aren’t thrilled with the changes, MLB hopes these steps will level the playing field and cut down on the use of illegal substances.