Under Rule 5.02(c) of the 2026 Official Baseball Rules (PDF pages 30–32), defensive infield alignments are regulated at two distinct moments of the pitching motion and locked across the half-inning. First, under Rule 5.02(c)(i), when the pitcher is on the rubber and begins the natural movement associated with delivery, the defense must have a minimum of four players (in addition to the pitcher and catcher) with both feet completely in front of the outer boundary of the infield dirt. Second, under Rule 5.02(c)(ii), at the instant the pitcher releases the ball, at least two of those four infielders must be positioned with both feet entirely on each side of second base.
The Inning-Long Side-Switching Prohibition and Penalty Structure
Rule 5.02(c)(iii) prevents clubs from rotating their best defender from the left side of the infield to the right side depending on whether a left-handed or right-handed batter steps into the box: from the moment the pitcher releases the first pitch to the first batter of a half-inning, the two infielders on each side of second base may not switch sides or move to another position on the opposite side of the infield for the entirety of that inning, unless a defensive substitution occurs (other than a pitching change substituting a pitcher for a player not already in the game). If a violating infielder is the first player to touch a batted ball, the batter is awarded first base without liability to be put out and all runners advance one base—unless the play naturally results in the batter reaching first and all runners advancing at least one base—while in any other violation circumstance the pitch is called a "ball" and the ball is dead (subject to the offensive manager’s right to accept the play on a sacrifice fly or bunt).
Anti-Circumvention Comments and Conditional Shading Trade-Offs
The Official Baseball Rules Comment to Rule 5.02(c) reinforces that these provisions are intended to prohibit clubs from alternating individual fielders across second base from batter to batter without making a substitution, and leaves to the umpire’s judgment whether an infielder who fails to reach the outer dirt boundary before the next pitch was attempting to circumvent the rule. Within those legal boundaries, defenses face a conditional shading choice: pinching the middle infielder close to the second-base bag takes away up-the-middle grounders after release, but widens the gap between the two fielders on the pull side if a hitter pulls a hard groundball toward the foul line or shoots a ball into the opposite-field hole.