A hostile species who live on the planet Nausicaa.
The Nausicaans are a tall, powerfully built humanoid species with heavy, ridged faces and protruding tusks. They have a reputation for violence and are often seen working as thugs, mercenaries and pirates in bars and trading posts on the fringes of known space.
The best known Nausicaan story is from Picard's youth. In 2327, just after graduating from Starfleet Academy, Ensign Picard and his friends got into a fight with three Nausicaans over a game at a recreation facility on Starbase Earhart. One of the Nausicaans stabbed Picard through the heart, and he needed an artificial replacement.
In the Next Generation episode Tapestry, Q gives Picard the chance to avoid that fight, and Picard learns that without the reckless streak behind it, he would never have become a captain. Nausicaans also turn up in Deep Space Nine, Enterprise and later series, usually as hired muscle.