Leeds United are facing punishment by the English Football Association after Sunday's Premier League loss to Manchester United was marred by a series of off-field incidents, including visiting player Anthony Elanga being hit on the head by an object thrown from the crowd.
Nine people have since been arrested and West Yorkshire Police issued a statement on Monday which said: "Officers were deployed in sufficient numbers to rapidly intervene to identify and arrest the people responsible and prevent any escalation in disorder.
"The majority of fans on both sides behaved appropriately throughout the match and there was no significant disorder, but we hope the early intervention and positive action ... will help send a very clear message."
Leeds said in a statement on Monday they were reviewing CCTV footage and would do "everything possible to find those supporters who are throwing objects on to the field of play,"
The statement continued: "Any supporter caught throwing objects on to the pitch will be issued a lifetime ban from attending our fixtures."
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The FA are awaiting an extraordinary incident report from match referee Paul Tierney in which the official is expected to address the disorder off the pitch which also saw pyrotechnic flares thrown from both sets of supporters and objects thrown at United goalscorers Harry Maguire and Fred prior to the incident which resulted in Elanga requiring treatment.
One supporter ran onto the pitch at the end of the game before being stopped by stewards, but Leeds could also face sanction for that incident.
Sunday's fixture was the first time the two clubs had met in a Premier League game in front of supporters at Elland Road for 19 years. Last season's game, following Leeds's promotion from the Championship in 2020, was played behind closed doors due to COVID-19 restrictions.
The long-standing hostility between the two clubs resulted in 900 police officers being on duty for the game -- a record for a Premier League fixture.
Sources have said that the FA will study Tierney's report before deciding on any action, which could range between a fine or partial closure of Elland Road.
Leeds will face an automatic £25,000 fine for failing to control their players after receiving six yellow cards during the game.