HS teacher/coach slapped my butt?

I’m not sure why this has been on my mind lately, but I’m unsure how to label it when my high school teacher/coach used to slap my butt while walking the hallways at school and at after-school practice. He made a few comments about my “big butt” sometimes while/after doing that. I remember feeling gross after, which was a major trigger of my eating disorder (always trying to shrink my butt). Was that inappropriate? How would people label that- sexual harassment?