While underway, commander/captain is judge, jury and executioner for disciplinary issues. They call it "Captain's mast" and the powers that come with it are wide and can be extreme, including demotions and docking pay.
The XO refused to receive the ship commander's punishment while on mission. Tantamount to a mutiny.
"A sailor drowned after being thrown into the sea when an 11-meter rigid hull inflatable boat (RHIB) flipped while being lowered into the water from amphibious transport dock USS San Antonio (LPD-17) on the first-in-class ship’s initial deployment. At the time, San Antonio was operating in the Gulf of Aden.
Ship commander Cmdr. Eric Cash received a letter of reprimand. The amphib’s executive officer, Lt. Cmdr. Sean Kearns, was found not guilty of negligence. Kearns had transferred from the ship when the Navy decided to levy a punishment. Instead of accepting non-judicial punishment, Kearns opted to fight a single charge of negligence in a military court. During the trial, according to news reports, his lawyers presented information detailing how, at the time of the incident, San Antonio remained an unfinished vessel with thousands of faulty welds, engine trouble and only a portion of the standard technical manuals typically found onboard. Kearns’ promotion to commander, which had been delayed pending the trial, took effect after the verdict."
That's nothing to do with mutiny at sea, or mutiny at all.