RCW 10.31.100
Arrest without warrant.
*** CHANGE IN 2021 *** (SEE 1320-S2.SL) ***
A police officer having probable cause to believe that a person has committed or is committing a felony shall have the authority to arrest the person without a warrant. A police officer may arrest a person without a warrant for committing a misdemeanor or gross misdemeanor only when the offense is committed in the presence of an officer, except as provided in subsections (1) through (11) of this section.
…
(2) A police officer shall arrest and take into custody, pending release on bail, personal recognizance, or court order, a person without a warrant when the officer has probable cause to believe that:
…
(d) The person is eighteen years or older and within the preceding four hours has assaulted a family or household member or intimate partner as defined in RCW 26.50.010 and the officer believes: (i) A felonious assault has occurred; (ii) an assault has occurred which has resulted in bodily injury to the victim, whether the injury is observable by the responding officer or not; or (iii) that any physical action has occurred which was intended to cause another person reasonably to fear imminent serious bodily injury or death.