When jumping or riding an unpredictable or predictably unreliable horse, many riders choose to wear protective vests in case of a fall.
Some stables require them for jumping students.
Vests are mandatory in many cross-country competitions, and they are a good idea for rough rodeo riding.
Some horsemen even wear them when working with unruly horses on the ground, to lessen risk of injury from being struck or trampled.
See also Safety