Mr. Mertyle has both Milwaukee Braves and Atlanta Braves memorabilia in his house. In 1962, the Braves were still playing in Milwaukee and had not yet made the move to Atlanta. This move wouldn't occur until three years later, in 1965.
Right after the first Wendy Peffercorn scene, when Squints and Yeah-Yeah are on the sandlot running towards the everyone else in the dugout, it's morning (at around 11 mins) with long shadows from left to right (from home to 1st base), but when they get to the dugout it's the afternoon (at around 29 mins) with shadows from right to left (from 1st base to home).
At the end of the movie when adult Smalls is calling the game and Benny is stealing home, in the monitor behind Smalls you can clearly see Benny is sliding into home, but the in the next scene he is still running towards the plate.
When the adult Benny steals home to win a game for the Dodgers, watch the monitor behind Scott Smalls in the broadcast booth. While Smalls is describing what is happening, the monitor shows Benny sliding safely across home plate (at around 1h 35 mins).
When Benny is writing the fake signature of Babe Ruth on the new baseball, one of the kids mocks Benny's autograph attempt and says "Baby Ruthey?" (at around 1h 01 mins) before he had completed his misspelling ("Ruthe", see 01:01:45 for spelling).
The first time we see Wendy walking in her green dress, her hair is straight. After a brief cutaway, her hair is curly and in a different position. (at around 31 mins) Her hair on either side falls behind her back where it looks straight because we can't see any of its ends. As she gets closer (at 33:40, 33:42, and 33:49) the hair on her left side falls in front of her shoulder and its wavy ends can be seen.
When the adult Smalls is telling the story of Babe Ruth in the beginning of the movie, there is a shot of the field from the box when it is almost completely covered in shadow with the sun from behind the box (at around 1 min). The next shot of the pictures on the wall however, there are shadows coming from the frames which can only happen when the sun is facing the box.
When Benny slides to get the baseball from Hercules, he grabs it with his right hand (at around 1h 21 mins). When he gets back up and runs though, the ball switches to his left hand (at around 1h 21 mins).
When Benny's fly ball knocks Scotty Smalls down (at around 7 mins), the camera switches from Scotty to a shot of the rest of the boys laughing (from 07:08 to 07:11), as the catcher, Ham, at home plate walking toward 1st, drops his glove (at around 10 mins) and starts to reach down (at around 11 mins) as the glove rolls away from him. But the next shot, showing Ham, Squints, Benny, and Yeah-Yeah (from 07:12 to 07:13), starts with Ham already standing upright with his glove on his left hand, looking out to left field (where Scotty has fallen) and then raising his mask with his right hand.
When Squints is in the pool with boys he is wearing his glasses but when he climbs up to ladder to leave the pool to head to the diving board you can see if you look close that his glasses are off but moments later while walking toward the diving board they are back on until he takes them off until just before he dives in.
When the kids are playing ball in the school yard, Benny hits a long ball with his shadow on the left side (our left at 01:51). When he starts running, the shadows switch to the right side (our right at 02:04).
When the kids are kicked out of the pool, they gather their clothes and run, but Tommy just runs without picking up clothes (at around 33 mins). In the next shot, he is running with an armful of clothes (at around 45 mins). Both Tommy and his older brother, Timmy, are wearing plaid trunks with white trim and both run off (at around 33 mins) without picking up cloths.
When the boys are jumping out of the tree house before the vacuums blow up, Benny is seen (at around 1h 08 mins) jumping over Ham who is holding onto the ladder, then Ham lets go and falls off (at around 1h 08 mins). In the next shot (at around 1h 08 mins), however, Benny and Ham hit the ground at the same time even though Benny jumped off way before.
When Benny is running from the Beast into the gymnasium/theater, he leaves the right door open. However, during the next shot where the Beast breaks through the left door's window, the right door is closed (at around 1h 23 mins).
The film is set in southern California, but filmed in northern Utah (in the suburban area around Salt Lake City.) There are several goofs throughout the movie that point this out, the most glaring of which being a Romney sign (see Trivia), and the appearance of Vincent Drug, which is a family-owned business in Midvale, Utah (a Salt Lake suburb.)
In the movies opening scene, adult Scott narrates that Babe Ruth's called shot happened in the bottom 9th inning in Game 3 of the 1932 World Series with the tying run on base. This would imply that the Yankees were down by 2 runs at Yankee Stadium in the Bronx. However the game was played at Wrigley Field in Chicago, and it was in the top of the 5th in a 4-4 tie where Ruth hit his called shot.
The end credits give thanks for the use of clips for a movie called "The Wolfman" (this is the movie being watched in the auditorium during the beast chase scene.) This film, however, is actually called "The Wolf Man" (with "Wolf Man" as two separate words.)
At several points in the movie we see lights on at Mr. Mertle's house. However, Mr. Mertle is blind and lives alone, so having lights on would be useless to him. However, contrary to popular belief, most people who are legally blind still retain a small amount of residual vision, and they do tend to rely upon it in their everyday lives. Thus, Mr. Mertle having the lights on in his house to assist with what little vision he would have left is not an error.
When the baseball team shows up to challenge the kids at the sandlot, Squints goes to throw his glove down and winds up going straight back into Tommy "repeat" Timmons' chest. If look carefully you can see Benny look back to see what happened.