In the opening sequence of the Boyz making their way to the beach, Jay goes from bare feet, to white slip on shoes, to bare feet again.
When Jay and Tony are in the bedroom with the two girls a stuffed animal is thrown and lands on the nightstand in front of the lamp. Tony's father comes in moments later asking about the smell in the air and the stuffed animal is gone.
After Jay meets with Stacy and Kathy on Bicknell Hill, Stacy already has his 1972 Squareback car, but as he comes home in the next scene, he is riding his bicycle from the beginning of the movie.
At the end of the movie before tony Alva performs the front side air, Stacy is seen in the background standing, then when the camera angle changes and the scene pauses, he is on his knees petting one of the dogs.
The first time the Z-Boys skate Sid's pool there is a skateboard left on the steps that changes positions several times.
When the team get in to an argument with the judge at the first skateboard competition when Stacey is disqualified, Skip says "our boys are kicking your girls' asses". What he should have said is "our girls are kicking your boys' asses". In reality, when the team went to the comp, the female members of the Zephyr team were outperforming the other male competitors, and this is what the character was actually trying to say. This is explained in the Dogtown and Z boys documentary.
When they are making skateboards at the shop the song mongoloid by Devo is playing which came out in 1978 and the movie takes place around 1976.
When Jay is riding down the street with no shirt on, his shadow changes from nothing, to a full sized shadow.
When a fight breaks out in a nightclub, one of the band members can be seen wearing a Black Flag shirt. This scene occurs in either 1976 or 1977, but Black Flag did not actually take the name Black Flag until 27 January 1979 (from 1976-1978 the band's name was Panic). Additionally, the song that is playing is a cover of the song Nervous Breakdown by Black Flag, which was not released until 1978.
Early in the film, there's a scene where Jay, his mom and Sid are eating at the restaurant where Stacy works. Sid offers his American Express card to cover the meal. When the card is handed over, you can clearly see a magnetic stripe on the back. Magnetic stripes didn't exist on credit cards in the 70s.
Stacy makes an appearance in 'Charlie's Angels', a show which aired between 1976 and 1981. The episode she appears in is slated as "Episode # 93" which would make it 1979 (the year in which the real Stacy Peralta appeared in the show). Later, a TV newscast mentions the fire that finally devastated the partially-ruined (and out-of-operation) theme park, Pacific Ocean Park, that was built on and around the Ocean Park Pier. That catastrophic blaze (and there had been minor ones before it), actually happened in 1974, and had led to the demolition/removal of the theme park's remains in 1975.
The wide 7-ply laminate concave skateboard that Tyson the bulldog rides at the championship was not available in 1977. Laminate decks existed but they were flat and narrow. Skateboards in 1977 rarely exceeded 7-8 inches wide. Tysons board is obviously a 10 inch wide mid to late '80s pool/ramp model with wider trucks and "new school" wheels.
In the scene after the boyfriend of Jay Adam's mother leaves her, Jay Adams is sitting on a couch in an alley and then begins to skateboard. Very shortly after starting, the character ollie's onto a swivel chair. The time frame in the movie at this time is 1975. This trick did not exist yet in skateboarding. The ollie was first invented on vertical skateboard ramps by Alan Gelfand in Florida in 1978. The "flatland ollie" (which was performed by the character in this movie in this scene) did not exist until 1982. In 1982, while competing in the Rusty Harris contest in Whittier, California, Rodney Mullen debuted an ollie on flat ground, which he had adapted from Gelfand's vertical version by combining the motions of some of his existing tricks. Mullen used a "see-saw" motion, striking the tail of the board on the ground to lift the nose, and using the front foot to level the board in mid-air.
When the boys are sitting across the street from the girls house, Jay is rolling the window up and down. When he rolls it up one last time, the camera is visible.
When Jay Adams is skateboarding in the giant cylinders, you can see the shadow of the cameraman following him for a brief moment.
During one of the surfers' waves at the cove, the yellow helmet is visible of a cameraman.
Around 10 min, The camera's shadow can be seen on the ground for a split screen, during a low shot of the skateboard.
When Stacey and Kathy leave after the first competition, they get in his car, and Stacey exclaims the Skip called him bro, and said, "You look hungry, bro." When really, Skip had said, "Hey, bro, you're lookin' hungry."