Terrence Williams was arrested on Sunday in Kent, Washington after making alleged threats to the mother of his child while also brandishing a gun, according to police.
At about 1:55 p.m., police were called to the home of the victim, who has a 10-year-old son with Williams, who was there for a scheduled visitation.
An argument broke out in the parking lot and Williams allegedly took out a gun.
Williams left before police arrived, but he was later taken into custody.
The Celtics signed Williams to a 10-day contract in February and was eventually signed for the remainder of the season and all of next season. Williams' contract becomes guaranteed if he isn't waived before Oct. 31.