Up to 300 Newcastle fans have been accused of causing trouble outside the DW Stadium prior to their 2-1 loss at Wigan on Sunday.
Magpies supporters are believed to have disrupted a number of amateur matches taking place near the away end of Wigan's home ground after heading over from their coaches to watch Wigan Cosmos versus AFC Leigh Centurions in the South Lancashire Counties League.
Between 250-300 fans ran onto the pitches, dropped their trousers, ripped out the nets and tried to break the goals by hanging on the crossbars, a Cosmos spokesman said. They also went on to boast about their actions, which included stealing a £65 match ball, on social networking sites after the game.
"As the supporters spilled out of the coaches, which were not managed by the club or police officials, they proceeded to watch the game from the touchline,'' the Cosmos spokesman said. "Some fans then chose to run on to the field of play, dropping their pants, causing the game to be stopped. The situation then magnified as a crowd of around 250-300 Newcastle United fans followed suit. Although good-natured at first, the fans then started to rip out corner flags as they ran over the pitches and also took the match ball. We never recovered the ball, though we did manage to recover the corner flags.
"The so-called fans then decided to charge over to the adjacent pitch where Goose Green Reserves were entertaining Olympic AFC in another South Lancashire Counties fixture. They again began by ripping out their corner flags. The fans then charged into the goalmouth, jumping on to the goalposts in an attempt to snap the crossbar with the sheer numbers clambering on them. They then started to rip the nets from the posts, tearing them and trying to take them. Our players helped to retrieve the nets. After spending quite some time singing and hanging on the goalposts, the fans then ran back over to our pitch whilst singing 'We're Newcastle United, we'll do what we want'.''
The spokesman added: "Once again I would like to stress that, despite the obvious scenes developing, no support was provided from the authorities. This incident was a very distasteful experience that lasted for over 40 minutes and with families, dads, granddads and youngsters all watching the games as well as some quite experienced players who were all left shaken.''
Cosmos claim the cost of replacing the ball and the damaged nets stands at £200 - a small amount for a Premier League side but a lot of money for an amateur non-profit side, the spokesman said.
He added: "The fact that these same fans have taken to Twitter and YouTube to boast about the incident and in fact revelling in it, showing no signs of remorse, is possibly even more disturbing. Not only have they cost my football team a great deal of expense but they have shown a total disrespect to football itself."
Newcastle have issued a statement condemning the behaviour of their fans, calling it "unacceptable'' and confirming they would reimburse Wigan Cosmos for the cost of the damage caused.
The statement said: "Newcastle United are very disappointed with the behaviour of a minority of its fans who were involved in the vandalism of equipment belonging to Wigan Cosmos Football Club and pitch incursions during their game against AFC Leigh Centurions on Sunday 17th March which caused the match to be stopped. Our travelling fans have a very good reputation, but the actions of a minority on this occasion were wholly unacceptable.
"Football, at all levels of the game, deserves the same degree of respect whether it is played in the Premier League or at the grassroots level. We were sorry to learn that this South Lancashire Counties Premier Division game was disrupted in this manner and we would urge anyone who witnessed this incident to contact Greater Manchester Police.''
A further statement on the club's Twitter feed thanked those fans who had reacted positively to the disturbances and pledged to reimburse Wigan Cosmos.
"Thank you for all of your positive efforts and warm wishes towards @WiganCosmos. Newcastle United will be covering the club's costs £NUFC''
Information from the Press Association was used in this report