# Rotating bone causes distortion in unrelated object

blender noob here so bear with me. I'm having trouble rigging the left arm of my character. For some reason, rotating any bone in the left arm distorts the brim of the character's hat. I created the left arm by duplicating the character's right arm (which rotates fine) and mirroring it. I then joined the left arm to the character mesh. I then select the character body then armature press ctrl + p and select Armature Deform with Automatic Weights. I try rotating the left arm, and the hat rotates with it (without distortion). I click on the left arm's hand bone and erase the weights in the hat that may be causing it to rotate with the arm. However, after doing so rotating the left hand bone causes the hat to rotate except with distortion (see picture). . I don't know why the left arm is behaving differently than the right arm since I pretty much copied it over. I have included the blender file too