Reversal was required where trial court erred in instructing the jury on “mutual combat” for purposes of self defense. Maria and appellant Ross engaged in a heated verbal discussion, and then Maria slapped Ross. Ross responded with a blow which fractured Maria’s cheekbone. At his second trial for battery causing serious injury and assault by means likely to produce great bodily injury, the trial court instructed the jury on the doctrine of “mutual combat” as it affects a plea of self defense. On appeal, Ross challenged this instruction, which told the jury that one cannot successfully plead self-defense if he was engaged in “mutual combat” with the victim. The court also refused the jury’s request during deliberations for a legal definition of mutual combat. The appellate court reversed Ross’s conviction. The instruction combined with the court’s instruction to the jury to rely on the ordinary meaning of mutual combat allowed the jury to suppose that any exchange of blows disqualified the participants from claiming self-defense. In fact, the doctrine only applies to a violent confrontation conducted by mutual consent, or an agreement to fight. Since the evidence here did not establish an agreement, and there was a substantial basis for the jury to believe Ross acted in self-defense, it was reasonably probable that a properly instructed jury would have returned a different verdict.