It has been called the most significant series of Major League Baseball rule changes in decades. On Thursday, they will make their regular-season debut.

Players, coaches and managers have been getting used to the bigger bases, pitch clocks and ban on infield shifts during spring training. Many fans will get their first taste of the changes this week as the 2023 campaign begins.

Here's a quick look at what will be new and different on Opening Day.


The pitch clock will be used to speed the pace of play. A 15-second clock will be used when bases are empty and a 20-second countdown will be used if there is a runner on base.

After receiving the ball, the pitcher must begin his throwing motion before the clock expires. A batter must be engaged in the batter's box and alert to the pitcher with at least eight seconds left on the clock.


There will be a return to more traditional infielder positioning under the new rules. Teams will no longer be able to use the infield shift — moving players across the diamond — with second base serving as a dividing line.

Two infielders must be on each side of second base when a pitch is delivered. Infielders must also have both feet within the outer boundary of the infield at the time.


Bases are slightly larger this season. They are 18 square inches, up from the standard 15 square inches in the past.

Home plate remains the same size. The changes could lead to more stolen base attempts and aggressive base running.