Wis. Stat. § 972.03
Each side is entitled to only 4 peremptory challenges except as otherwise provided in this section. When the crime charged is punishable by life imprisonment, the state is entitled to 6 peremptory challenges and the defendant is entitled to 6 peremptory challenges. If there is more than one defendant, the court shall divide the challenges as equally as practicable among them; and if their defenses are adverse and the court is satisfied that the protection of their rights so requires, the court may allow the defendants additional challenges. If the crime is punishable by life imprisonment, the total peremptory challenges allowed the defense shall not exceed 12 if there are only 2 defendants and 18 if there are more than 2 defendants; in other felony cases 6 challenges if there are only 2 defendants and 9 challenges if there are more than 2. In misdemeanor cases, the state is entitled to 3 peremptory challenges and the defendant is entitled to 3 peremptory challenges, except that if there are 2 defendants, the court shall allow the defense 4 peremptory challenges, and if there are more than 2 defendants, the court shall allow the defense 6 peremptory challenges. Each side shall be allowed one additional peremptory challenge if additional jurors are to be selected under s. 972.04(1).
Wis. Stat. § 972.03
A defendant is not entitled to a new trial when both the prosecution and defense are given an equal number of peremptory strikes, even if the number is less than provided for by statute. State v. Erickson, 227 Wis. 2d 758, 596 N.W.2d 749 (1999), 98-0273.