Officers responded to the 3200 block of 18th Street in Everett at about 7:30 p.m. after getting a call about two men fighting outside an apartment complex.
When they arrived on scene, the officers found a man who had been slashed with a machete, according to Aaron Snell with the Everett Police Department.
The victim was taken to Harborview Medical Center for treatment. His current condition is not known.
Snell said two baseball-bat wielding brothers had been fighting with each other outside the apartment complex when a third man approached them to break it up.
Police are still trying to figure out what exactly happened next, but they believe the third man took out a machete and slashed one of the brothers.
Police and a K-9 unit searched the area and found a 47-year-old man believed to be the attacker. He was taken into custody for questioning. The man told police he was acting in self defense, according to Snell.
Police also responded to a second, unrelated slashing Wednesday night. In that incident, a woman walked into a local Safeway with a slash wound to the neck.
Police believe that attack may be a domestic violence incident, but they're still looking for the slasher.