When Shawn arrives at the night club following his first fight, he steps out of the car clearly sporting two bruises on his face. After the scene shifts to the interior, his bruises have all disappeared.
At about seven minute in, Shawn MacArthur crosses the road under heavy rain with a wet box. A minute later, after he gets his money back from Harvey Boarden, he's back on street where there is no water, no rain, and his box is fully dry.
When Harvey pays a visit to Jack's office in the back of the store, Harvey knocks on the door then proceeds to enter the room. In the next shot, one of Jack's men opens a second door for Harvey and there is a wall and a clothes rack behind Harvey.
In the last fight of the film, Shawn rams Evan into a wall, which caves in from the impact. When Evan pushes back, Shawn reaches out for something to grab and accidentally pulls down the "crumbled" section of wall (actually a thin sheet that had been placed over the real one), exposing it as a special effects prop.