Continuity mistake: It is established that "The Sandlot" is a relatively vacant lot, mostly dirt, with grass mostly in the infield areas. But numerous times in the scenes involving trying to retrieve the baseball, the background shows a manicured yard with a yellow house just off to the side. It's not in the distance, it's right next to the treehouse. And it doesn't appear that this is just another angle, as we see the treehouse from a distance numerous times, and there is no grass or house anywhere in its area, let alone a full back yard with a grill.
Continuity mistake: A while into the chase scene at the end of the movie, the dog chases Benny through the founders' celebration. A large cake, about four or five tiers high, is being carried by a couple of bakers. They lose their balance and set the cake down, but eventually it gets sent into the air. While going up, it stays whole, but the shot changes when it's coming down, and it has now broken apart into many small pieces.
Continuity mistake: After Squints kisses Wendy and the boys leave the pool area, Ham asks Squints if he planned it, and he looks back at Wendy. When the shot changes, some of the boys change position. For instance, Timmy is standing before the shot change, but sitting immediately afterward.