Puukkojunkkari (or häjy, Swedish: knivjunkare, translated to English as knife-fighter; literal translation: "knife junker") was a term used of troublemakers who were active in the Southern Ostrobothnia region of Finland in the 19th century. Fights among puukkojunkkaris were common, and often resulted in homicide; one could even get stabbed at a funeral. Puukkojunkkaris usually made trouble at weddings, stole horses and circulated among towns and villages. They also participated in gambling, thievery and courtship with women. The most notorious puukkojunkkaris lived in towns near the Lapuanjoki river, such as Alahärmä. The first homicides happened in the 1790s, but the famous "golden age" of puukkojunkkaris lasted from the 1820s to the 1880s.
Puukkojunkkaris were present in all society classes. They included both free houseowners and farm servants. The houseowners were often gang leaders. Puukkojunkkaris were often feared and respected, and fought for their honour. The code of honour disallowed fear and respected fighting. Puukkojunkkaris were often difficult to prosecute because few people dared testify against them. Puukkojunkkaris also received admiration and respect because they dared to stand up against society and authorities.
Many attempts have been made to explain the rise of puukkojunkkaris. In the 19th century, the living standard in Ostrobothnia rose, and because of this, weddings became grandiose events with lots of alcoholic beverages. Young men in Ostrobothnia did not often get a chance to inherit their own farm in their home town and earn their own wealth, which led to frustration.
Reino Kallio’s theory of knife-fighters is based on the idea of a counter reaction caused by social control that has been taken too far. He sees youth’s violent behaviour as a protest-like rebellion against the pressure exercised by the power structure; particularly against local laws and parish discipline. The resistance that started as little more than slight mischief became branded as troublemakers and led to a path towards serious crimes. This was particularly due to the fact that parish discipline, which was stricter than general law, lowered the threshold of crime. At the time, there were many new ways of youngsters spending their free time, such as wandering around outdoors at night, which was considered a breach against the curfew and a threat to the existence of class society. Therefore, district courts started punishing people for curfew at night – as well as for other breakages against parish discipline.