Five men ended up in hospital after violence flared in Staines Road, beside Hounslow Heath, where a car boot sale was taking place on the morning of Sunday February 28.
Seven people were arrested and four men eventually charged, each with one count of violent disorder and one of possessing an offensive weapon in a public place.
They all denied the charges and were due to stand trial on June 27 at Isleworth Crown Court.
However, the court said the charges were dropped against three of the defendants - Charlie McDonagh, 42; Brian McDonagh, 20; and a 17-year-old who cannot be named, all of whom lived in Manor Waye, Uxbridge - after the prosecution failed to offer any evidence.
A fourth man, Charles McDonagh, 23, also of Manor Waye, denied the original charges, which the court said would be left to lie on file, but admitted a lesser offence of section four public disorder.
He is due to return to the court for sentencing on December 16.
Armed fight led to ban on sale of power tools
Police said the disorder had first flared that morning, at around 7am, in the car park of the car boot sale.
They said a fight broke out there and one man was stabbed and deliberately run over, breaking his leg and fracturing his skull.
Soon after, police said three vehicles were involved in a collision in Staines Road, Hounslow, and an armed fight erupted between the occupants.
The organisers of the car boot sale said at the time that the fight had not broken out at their event.
The disturbance did, however, lead police to agree a voluntary ban on the sale of power tools with the organisers of that event and other car boot sales in the borough.