Roy Halladay, a Hall of Fame pitcher, had a dangerous mix of amphetamine, morphine and other prescription drugs in his system and was doing acrobatics in his amphibious sport plane when it plunged into the Gulf of Mexico off Clearwater, Fla., killing him on Nov. 7, 2017, the National Transportation Safety Board said on Wednesday.

A 13-page report said Mr. Halladay had 10 times the generally recommended level of amphetamine in his system, as well as an antidepressant, a muscle relaxant, a sleep aid and morphine, an opioid pain medication, when he lost control of his plane and crashed nose-first into the water.

Mr. Halladay, who was 40 and had bought the plane a month earlier, died of blunt force trauma and drowning, the report said. An avid pilot, he had been known to enjoy stunt maneuvers in the airplane, an Icon A5, the report said.

Just days before his crash, he had flown under the Skyway Bridge, which has a 180-foot vertical clearance over the water, the report said. A few days later, the report notes, he wrote on Twitter that “flying the Icon A5 low over the water is like flying a fighter jet!”