Ironically, the worst thing I ever saw a coworker do was to change a function that accepted an Integer value between 0 and 32767 to one that accepted a Float between 0.0 and 1.0. Perfectly sensible change except that it resulted in a 120 mph knuckleball fired a foot above a 10 year old kid’s head, followed by a fist fight between the client and my boss.
That sounds like something that should have been caught by QA, integration tests or unit tests long before it was launching balls at ten year olds.
Yes, testing the new Little League control module on a field full of Little Leaguers was not the best plan.