Footage circulated on social media of the yob, believed to be a Portsmouth supporter, swinging a fist at the animal as police attempted to control violent crowds following Southampton’s 4-0 Carabao Cup win over their arch rivals.
A stunned onlooker recording the incident can be heard shouting: “He’s swinging for a horse! He’s swinging for a horse! Is he mad?!”
After the cowardly act, the perpetrator attempted to escape the wrath of the authorities by running away from the scene.
However, he was unsuccessful in doing so, with the police rider and horse chasing the man down the road before he ran into a unit of riot cops.
He was subsequently pinned down to the floor and restrained by a large number of officers who were present.
Earlier, rival supporters clashed in fiery scenes ahead of kick-off on the south coast.
Footage captured by one man shows one police officer being thrown to the floor as Portsmouth and Southampton fans went head-to-head for the first time in seven years.
Large numbers of police were present who attempted to separate both sets of supporters and guide them safely into the ground.
Coins, bottles and smoke grenades were among the objects thrown as the shameful scenes of violence broke out.
It was the first meeting between the two sides since April 2012, with a red hot atmosphere both inside and outside the ground.
Danny Ings notched a first-half double, while Cedric Soares and substitute Nathan Redmond were also on target for Ralph Hasenhuttl’s men as they eased past the League One strugglers on the night.
Hampshire Constabulary said prior to the game this would be their largest-ever football policing operation, owing to the high possibility of violence occurring on the night.
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The emergency services used horses, dogs, helicopters and drones to disperse the angry crowds.
Police said a total of five men were arrested, including a 42-year-old on suspicion of animal cruelty.