A Watchdog pit bull is an American pit bull terrier from a particular lineage called the Watchdog bloodline. The Watchdog bloodline is an older lineage within the breed, but its thick build has led to it being classified among the new-style American Bully lines.
Watchdogs were originally bred by mating Carver and Mason line dogs of the American pit bull terrier breed. They were bred and trained to hunt wild hogs. Since wild hogs can weigh up to 600 pounds, and dogs that hunt pigs must hold them at bay or physically latch on to them, dogs bred to hunt this kind of game must be powerful and strong. The Watchdog line is noted for its strength and agility, as well as for having a large head and a somewhat heavier build than so-called "classic" pit bulls. The later Bully lines, developed since the late 1990s, are dogs with large, blocky heads, prominent musculature and thick, heavy bone structure, which has led the Watchdog line to being classified among them despite dating from decades earlier.