First define the field ... then the playing field / dead ball territory.
The the penalty for stepping into dead ball territory with both feet.
SECTION 2 THE FIELD ART. 1 . . . A diamond (or infield) shall be a 90-foot square. When measuring the distance to first base and third base, measure from the apex of home plate to the back edge of the base. The outfield is the area between two foul lines formed by extending two sides of the diamond as in Diagram 2. The infield and outfield, including the boundary marks from home plate to first and third and their extended foul lines, are fair ground. All other area is foul ground.
SECTION 42 PLAYING FIELD The playing field includes both fair and foul territory. Any other areas beyond the playing field are defined as being outside the playing field (dead ball area). Any wall, fence, barricade, rope, wire, marked or imaginary line is -considered a part of the playing field. Any areas beyond those boundaries are outside the playing field.
SECTION 1 DEAD BALL ART. 1 . . . Ball becomes dead immediately when:
i. a fielder, after catching a fair or foul ball (fly or line drive), leaves the field of play by stepping with both feet or by falling into a bench, dugout, stand, bleacher, or over any boundary or barrier such as a fence, rope, chalk line, or a pregame determined imaginary boundary line; or