What are the limits on defensive shifts?

Since 2023, MLB limits defensive alignments:

• The four infielders must be within the boundary of the infield when the pitcher is on the rubber.
• Infielders may not switch sides, so a team cannot move its best defender to the side of the infield where the batter is likelier to hit the ball.
• The rule does not stop a team from placing an outfielder in the infield or in the shallow outfield grass in certain situations, but it prohibits four-outfielder alignments.

Penalty (from the 2025 season): if there is a violation and the violating player is the first to touch the ball in play, the batting team may accept the result of the play or the batter is granted a free base, which lets other runners advance one base. Before 2025 the choice was the result of the play or an automatic ball.

Source: MLB, Defensive Shift Limits (mlb.com/glossary/rules/defensive-shift-limits).