In one scene Pete Dunham is seen wearing an Adidas track jacket that was made for the David Beckham line. Being such a die hard West Ham fan and being that Beckham played for Manchester United there is no way that Dunham would wear any attire associated with Beckham.
During the first bar scene when Bovver is shown standing on a table singing their West Ham song, he is clearly shown drenched in beer as they throw it everywhere. The next scene is shown in the bathroom with Bovver and Matt and his sweater is completely dry and shows no signs of the beer throwing.
When Matt has the Chelsea grin, he is obviously bleeding a lot in the corners of the mouth. But in the next scene with the van and then with the fight, the blood is gone and it doesn't show and sign of wounds and him wiping the blood away.
At Matt's first fight (with the credit card) Pete is wearing a long coat. He is still wearing the coat in the van. But when the guy throws a stone at the van and they get out to fight, suddenly the coat is gone and he is just wearing his black vest.
At Matt's first game when Bovver goes to shout at the rival team, the guards take Bovver away, when Bovver resists his hood falls down. The next scene features him still resisting but his hood is back up. As his arms were detained there was no way for him to put it back up.
When Matt (Elijah Wood) goes to meet his sister Shannon (Claire Forlani) he gets off a Northern Line Train at East Finchley Station (in the open air) and is then seen walking down the steps from the platform, he walks down a subterranean passage, but he then walks out of the exit from Charing Cross Underground Station (a subterranean station) which leads out on to Trafalgar Square.
At Matt's first match, the away fans team are named as being Birmingham City (who play in all blue shirts and white shorts), and their supporters are referred to as "northerners". However, the team shown playing West Ham United is actually Gillingham (blue and black stripes with black shorts), who ironically are one of the few teams in England south of West Ham. The match shown was played on Saturday 27th March 2004, and finished 2-1 in favour of the Hammers.
(at around 1h 21 mins) When the Major is visited by his wife in the hospital, he starts crying towards the end of the scene. The trail of tears is shown running down his cheek which is not possible for a man lying in that position (it should trickle down the corner of his eye).
When Matt leaves Boston, a Delta Airlines jet is shown taking off, implying he is on board it. He is then shown arriving and an announcement can be heard saying welcome to Heathrow. At the time of the movie, Delta Airlines did not serve Heathrow.
During the scene where the motorcyclist is going through the tunnel to visit 'the enemy' in Millwall, the sign says "Welcome to Millwall, London Borough of Tower Hamlets". This is the area called Millwall in London Docklands (Isle of Dogs) and not where the football club is located as it moved south of the river many years ago from here. It is now in Bermondsey which is in SE16 area of London. Most of SE16 is in the London Borough of Southwark, but the part where Millwall is located comes under the London Borough of Lewisham.
As Matt arrives in London, he is seen on an underground train pulling into a station, with a sign saying 'Bank'. As he steps off the train it is clearly not Bank station, as the station Matt is at is an above ground station, which Bank is not. As Matt emerges from the Underground to meet his sister he is at the real Bank station in Central London.
In one of the first scenes in the movie, Matt's sister claims she has been trying to make him visit her for 3 years. Later on, Steve Dunham explains how 10 years ago, after being involved in the fight which killed Tommy Hatcher's son, Matt's sister saved him and turned his life around. It would not make sense that Matt's sister had waited 7 years before starting to convince him to visit her.