Monkey fists are illegal in the states of Massachusetts, California and New York. They are also outlawed in a number of other countries.
The monkey fist is a knot that is designed to form a large knot at one end of a rope. It has been used in many past maritime applications, such as securing a heavy object to a line, and is still popular in the decorative arts. Despite its popularity, it holds a dark history—enabling sailors to use it as a weapon, particularly against their fellow crew members.
This is the reason why it has become illegal in some states and countries. In Massachusetts monkey fists are illegal to possess or carry since 1960.
California outlawed it in 1973, and New York has prohibited it since the mid-90s. In other countries, it is also illegal, such as in Australia, where it is classified as a prohibited weapon.