Teen violence refers to harmful behaviors that can start early and continue into young adulthood. The young person can be a victim, an offender, or a witness to the violence. Violent acts can include: bullying, fighting, including punching, kicking, slapping, or hitting, and use of weapons such as guns or knives. Some violent acts can cause more emotional harm than physical harm. Others can lead to serious injury or even death. An important risk factor for violence in teens is the behavior of their friends and classmates.