Mom's an abuser.
And she does not have absolute authority. "Her kid" is not her property. The use of her power is supposed to wane as the child reaches adulthood. To use it so brutally at such a late age, especially if it's believed to be appropriate, means the boss mom screwed up raising him- probably by abusing her power all along, by the looks of it.
He's 17 and graduating. Using power has repercussions. At 18 he should walk out on her and let her glory in her power for a decade without him. If she misses him, she can hug the diploma she withheld, and revel in her "power."
That's just my way of saying she was a jerk, if you didn't catch that.
For all we know, Mom warned him prior to graduation. “If you do x, y will happen” If so, he did x, she stuck to her guns.
He is 17 and old enough to control his behavior in this type of setting if that is what his mother expected from him.
As I used to tell my own sons, if that is the worst thing that ever happened to you, I want your life.
You are so far off beam it is breathtaking. I sense a great deal of transference here. Your casual tossing about of terms like “abuser” and “brutal” diminishes the true abuse and brutality that exist. “Brutal” for making him clean the gym for his mockery???? Either you are “discovering” motives and actions that were not reported, or you have no clue about abuse and brutality.
There is nothing here to justify a charge of abuse. He behaveed inappropriately (name one 17 year old that doesn’t at some time or another) and Mom called him on it - as moms are supposed to do.