The Toronto Star in 1991 described this incident:
One of the sadder episodes in major league baseball was played out in the skies above Toronto more than a half-century ago.
In the very early morning of Sept. 17, 1935, Brooklyn Dodgers outfielder Len Koenecke was beaten to death by the pilot after becoming rowdy in a chartered airplane.
A few Dodgers were flying home from St. Louis to New York, rather than take the train. The 30-year-old Koenecke, who had a history of depression and a recent arm injury hampering his .283 season, had been put off a commercial airliner in Detroit for drunkenness.
He chartered a plane there, but would pay for it to go only as far as Buffalo.
Nearing Toronto, Koenecke suddenly attacked the pilot and then commenced a battle with the co-pilot, whom he bit and punched.
As the plane pitched around the sky out of control above what now is Etobicoke, the three men wrestled before pilot Joseph Mulqueeny finally was forced to hit the player over the head with a fire extinguisher. Repeated blows fractured Koenecke’s skull and he was dead before the plane crash-landed on the infield of the old Long Branch Race Track, around what now is Kipling and Evans Ave.
I’ve seen a few other news stories claiming Koenecke was the first airplane terrorist ever, but this episode hardly seems like terrorism to me. I first read about it in Bill James’ Historical Abstract from the mid-’80s, with James noting that Mulqueeny also had to fight off some angry dogs as he left the plane following the landing. Baseball players have been involved in a lot of ugly, violent incidents, but this one is maybe the most bizarre baseball death I’ve ever heard of.