Modiri participated in a group attack on the victim, and was convicted of felony assault. The jury found that Modiri personally inflicted g.b.i. on the victim. The jury was instructed pursuant to CALJIC 17.20 that the defendant must personally inflict the harm, and in the case of a group attack where jurors could not decide on which person inflicted the injury, the allegation could be sustained if the defendant applied physical force to the victim which could have caused the injury, or under such circumstances that the “cumulative effect” of the force used by all participants would have caused it. The appellate court held that CALJIC 17.20 prejudicially failed to require the personal infliction of g.b.i. The Supreme Court granted review on the issue of whether the group beating theories in CALJIC 17.20 satisfy the personal infliction requirement. The Supreme Court reversed the appellate court, finding that no instructional error occurred at trial. The defendant need not be the sole or definite cause of a specific injury where he physically joins a group attack and applies force to the victim sufficient to inflict g.b.i. CALJIC 17.20 adequately describes these principles, and a contrary approach that those who perpetrate mob violence and inflict gratuitous injury would evade enhanced punishment.