Dear Jean Graham,

Typical fighting behaviour between two stallions. This usually happens when a younger stallion attempts to abduct a young female (usually the dominant stallion's daughter) from the dominant stallion's herd. During the fight, one of the things they try and do is bite each other on the front legs. In the first picture, the stallions are both down on their knees in an attempt to prevent being bitten on the legs.

The other pics show various stages of fighting, with head displays showing teeth prior to biting attempts (4th pic), biting at neck and legs (2nd pic) and possibly the end of the fight, or maybe some movement prior to kicking with the hind legs (3rd pic).
The first pic in particular is a wonderful illustration of what happens when two stallions fight! Good photographs. :)

Good Luck! Lex Hes