If you injure someone intentionally, such as with a punch, they may sue you for medical costs, lost wages, and (for serious injuries) pain and suffering. If you believe it was self-defense, you can raise that as an affirmative defense, and if the court believes it was in fact self-defense, you should not be liable.Based on what you write, I do not think a court would consider this self-defense: it sounds as if there was a confrontation which you could be considered to have instigated, by jabbing him with a pencil. Also, self defense is not retaliastion--it is defense against an imminent or ongoing attack. If he punched you but that was that, you are not necessarily entitled to punch him back.