Same thing happened to college buddy who got beat-up by Chicago police and believe me they know how not to leave marks. Parents had same reaction (he is Hispanic)
I had an incident in HS where the cop told me to "run along young man" so I went home. Never told my parents.
I was roughed up by the Foster City PD when I was 18. They were on a training run and all 4 cops took turns. Not punching me but repeatedly throwing me up against the wall so as to spread ‘em.
They were mad that I did not have drugs on me!
In their defense there were very few blacks in that town. Crime was very low.