At the end of the fight at Grandma's Ranch where they are getting ready to take off in the helicopter you can hear the helicopter motor spinning up but the blades are clearly not spinning. The video cuts away and then back to them still not spinning however after the 3rd cutaway the blades are finally spinning.
When Alex and Tommy go to the Coliseum to search for Travis, and they question Weldon, he says the Coliseum is a dance club, period. Alex responds "Travis Brickley doesn't dance." Travis did plenty of dancing in Best of the Best.
In the arena Tommy Lee fights Khan who is with the nunchakus. Lying on his back, Tommy does a hop-up to kick Khan. In the first shot, it is clear that Tommy is rolling to his back after the kick. In the next shot, he does the same move but jumps to his feet instead.
During the fight between Tommy Lee and The Hammer/Boxer, Tommy punches him in the face causing blood to spill out of his mouth and onto his lips, but when Tommy is just about to follow up with a kick for a split second you can see that there is no blood on The Hammer's lips.
When Alex is driving with tommy and Walter on the highway with the wind mills after the thugs try and kill them the helicopter filming the scene is visible in the window of the ford explorer. You can even hear the helicopter,
As Walter is playing Tetris, he turns to his dad Alex and starts talking. The game on the screen continues like someone would still be playing it - several blocks move horizontally, rotate and then descend rapidly even after Walter has put the controller away.
If the Coliseum is a dance club that is a front for a secret, illegal, underground martial arts competition, then why do they have windows and television monitors throughout the club so that the people "dancing" can view the fighting action?
When Alex and Walter arrive at Sue's apartment after leaving Grandma's, she tells them she knows about Tommy fighting Barakus. If the fights are an underground, secret fighting competition, then how would she know Tommy would be there fighting?
The goof item below may give away important plot points.
During the gun fight scene at Grandma's ranch James get shot by one of the gunmen and his left little finger and left ring finger are blown off. In the next couple scenes when he's shot by other gun men you can see that his left hand is fully intact with his little finger and ring finger still attached. When James crawls across the car to stab one of the gunmen his little finger and ring finger are missing like they should be.