From Wikipedia

Bodyline - It's Just Not Cricket

Bodyline, also known as fast leg theory, was a cricketing tactic devised by the English cricket team for their 1932–33 Ashes tour of Australia, specifically to combat the extraordinary batting skill of Australia's Don Bradman. A Bodyline delivery was one where the cricket ball was pitched short so as to rise towards the body of the opposing batsman on the line of the leg stump, in the hope of creating legside deflections that could be caught by one of several fielders in the quadrant of the field behind square leg. This tactic was considered by many to be intimidatory and physically threatening.

Although no serious injuries arose from any short-pitched deliveries while a leg theory field was set, the tactic still led to considerable ill feeling between the two teams, with the controversy eventually spilling into the diplomatic arena. Over the next two decades, several of the Laws of Cricket were changed to prevent this tactic being repeated. Law 42 includes: The bowling of fast short pitched balls is dangerous and unfair if the umpire at the bowler's end considers that by their repetition and taking into account their length, height and direction they are likely to inflict physical injury on the striker...'

The occasional short-pitched ball aimed at the batsman (a bouncer) has never been illegal and is still in widespread use as a tactic.