Contrary to popular myths, many stallions do not live with a harem of mares. Nor, in natural settings, do they fight each other to the death in competition for mares.
Stallions that are kept from estrous (a regularly recurrent state of sexual receptivity during which the female of most mammals will accept the male and is capable of conceiving) mares tend to get frustrated and this frustration can be directed towards other horses, people and towards themselves.
Stallions are often considered ‘dangerous’ due to their reproductive behavior (hormones), but this behavior is greatly influenced by stallion management.
They are often kept away from mares completely, singly housed in a dark corner of the barn with little to no turnout. That is for sure that government and even stallion owners should try to change this situation and be aware of the danger that comes from aggressive stallions if they have not experienced it yet.