Why did Don Bradman retire?

Don Bradman was keen on cricket from a very young age: he spent many an hour practising his cricket using a stump and a Golf ball. Bradman developed his legendary split-second speed and accuracy by practising hitting into a water tank on a brick stand behind his home: when hit into the curved brick stand, the ball would rebound at high speed and varying angles. His exceptional skill developed out of these early years.