Definitions

1. noun

A person who is considered to be a bully or a troublemaker, especially in a gang or a group of young people.

“The local gang was notorious for having a gagster who loved to cause trouble in the neighborhood.”

2. noun

A person who engages in or encourages boisterous or rowdy behavior, often in a group or crowd.

“The concert was disrupted by a gagster who started a fight in the mosh pit.”