The most common reason for this is because you or somebody else has been feeding them titbits by hand. The horse starts to expect them and becomes annoyed if they’re not forthcoming.
The occasional polo or something is fine, but regular feeding by hand will only encourage him.
If he does bite (becomes nappy) then a light slap on the nose, a firm “No!” and definitely no titbit should teach him to behave better.
This is very noticable in the semi-tame Dartmoor ponies that are found near car parks and the road – many visitors get bitten because they’re always being fed by hand. Of course, this also encourages the ponies onto the road and results in many pony deaths a year.
