A brawl broke out at Haydock just as the final of eight races got under way.
Two distinct groups of men were throwing punches in among the general crowd, including women and children.
After the initial disagreement seemed to have passed, it then broke out again before security staff intervened.
A Haydock Park spokesman said: “We take a zero tolerance position on antisocial behaviour.
“The perpetrators were ejected at the time and we are continuing to work with the police on this matter.”
The issue of violence on racecourses captured the headlines last spring when fights took place at Goodwood and Ascot on successive weekends, with tracks subsequently implementing more stringent security measures.
Merseyside Police said one man had been arrested on suspicion of affray and possession of a controlled drug following the brawl at Haydock.
The force also asked anyone with information about the incident to contact police.
Oliver Hodgson said he believed there was “at least” 60 to 100 involved in the melee.
“It was something out of a horror scene, it was traumatic,” the 15-year-old racegoer from Gosforth, Copeland told the Press Association.
“The security tried to intervene but you couldn’t do anything at this point they had to sort of let them sort it out.
“There were families and kids there, they were bumping into prams and as you can see on the video there’s a mum and child being rushed off by security.
“Early on in the footage she gets pushed over.
“Everyone was so shocked because it was such a nice day and the weather was good and then it just turned.”
Oliver said he did not know how the fighting started.
“I just think it was a drunken mess to be honest, but I have to clarify this was a minority and this is not how everyone behaves at racing,” he said.
“Racing is not the type of event where this happens, racing events are amazing.
“There will be people there who think I’m never going to a race event ever again and that’s why things like this are so wrong.”
Oliver said police arrived shortly after and said he did not see anyone with serious injuries.