The film is told through the perspective of Scotty Smalls, who is reminiscing about the summer of 1962. Smalls moves with his mother and stepfather Bill to a new neighborhood outside Los Angeles and struggles to make new friends. One afternoon, he met Winnie the Pooh, Ash Ketchum, Simba, Baloo, Mickey Mouse, Tai,and their friends (whom Ash is bonding with him) and decided to follow a group of neighborhood boys, and he watches them play an improvised game of baseball at a small field, which they call the "sandlot." Smalls is reluctant to join their game because he fears he will be ridiculed based on his inexperience. Nevertheless, he chooses to play with them, but fails to catch a simple fly ball and properly throw the ball back to his infielders. All the other players, except for Benny Rodriguez, begin to laugh at Smalls for committing defensive miscues, prompting him to leave the sandlot in embarrassment. Benny, who is the best player in the neighborhood, shields Smalls from the insults of his peers and invites him to rejoin their game. He proceeds to give Smalls advice and helps him earn the respect of the other players.
As Smalls continues to play with the team, he begins to learn many of the customs of the sandlot, while experiencing many misadventures with his new friends. He learns that players avoid hitting home runs over the sandlot’s fences, as the property beyond them is guarded by a massive and ferocious dog, a 350-pound English mastiff called “The Beast.” One day, Benny hits a ball so hard, that he ruptures its leather, causing the ball's entrails to come out. The group cannot afford to buy another baseball, and is forced to retire for the afternoon. However, Smalls runs to Bill’s trophy room, and steals his stepfather's autographed ball, in hopes of preserving the game. The team is impressed with Smalls’ gesture, and allows him to have the first at bat with the ball. He proceeds to hit the ball out of the sandlot, but is shortly enveloped by fear once he realizes that he has lost Bill’s ball. The situation is further worsened when Smalls realizes that the ball was autographed by Babe Ruth, and is almost irreplaceable.
Smalls and his friends begin engineering elaborate plans to recover the ball from The Beast. After five failed rescue attempts, Smalls prepares to accept his fate. Around the same time, Benny has an enlightening dream, where he is visited by Babe Ruth, who encourages him to run into the sandlot, and use his speed to recover the ball and escape. Ruth leaves Benny with the words, “Heroes get remembered, but legends never die.” Benny rallies his friends the following morning at the sandlot, and prepares to recover Smalls’ baseball. Using his PF Flyers, he steals the ball from the Beast, and successfully manages to elude the dog as it chases him through town. At the end of the race, the Beast is injured after a fence collapses on it. Smalls feels responsible for the ordeal, and helps The Beast escape the rubble. After being rescued, The Beast, whose real name is Hercules, becomes much more friendly and affectionate towards the boys, even showing them where he had buried all the baseballs that had gone into the yard over the years. Benny and Smalls then decide to tell the dog’s owner, Mr. Mertle, about the ordeal. They eventually learn that Mr. Mertle was a professional baseball player with the Pittsburgh Pirates in 1927 and was a friend of Babe Ruth. Mr. Mertle, whose career ended after a hit by a stray pitch blinded him, agrees to give Smalls a ball signed by Murderer's Row – several of the best Yankee hitters in the late 1920s. In exchange, the boys are to visit Mr. Mertle once a week to talk about baseball. Smalls proceeds to give his stepfather the ball that Mertle gave him.
While Bill is pleased with the Murderer's Row ball, he is still upset about the Babe Ruth ball, but he only grounds Smalls for one week. Smalls goes on to explain what became of all his friends, and the future careers they pursued. The film then jumps 30 years into the future, where Smalls is a radio commentator for the Los Angeles Dodgers, and Benny “The Jet” Rodriguez is one of the team’s star players. While he is in the twilight of his career, Benny manages to steal home in the movie’s final moments, before flashing a thumbs-up to Smalls in the press box.
- Ash Ketchum, Pikachu, Misty, Togepi, Brock, Littlefoot, Cera, Ducky, Petrie, Spike, Chomper, Ruby, Guido, Grandpa Longneck, Grandma Longneck, Skip, Mr. Thicknose, Bloom, Stella, Flora, Musa, Tecna, Layla, Simba, Nala, Timon, Pumbaa, The DigiDestined and their Digimon, Baloo, Bagheera, King Louie, The Vultures (Buzzie, Flaps, Dizzy, and Ziggy), Jiminy Cricket, Zazu, Kronk, Mickey Mouse, Pluto, Sora, Donald Duck, Goofy, Bugs Bunny, Daffy Duck, and Ttark guest star in this film.
- This is an NTSC film with NTSC bits from the Winnie the Pooh films, the Garfield films, The Little Mermaid II: Return to the Sea, the Ice Age films, Whispers: An Elephant's Tale, the Star Wars films, the Aladdin films, the Pokémon films, Winx Club: The Secret of the Lost Kingdom, The Lion King films, Digimon: The Movie, The Jungle Book 1 and 2, Talespin: Plunder and Lightning, Pinocchio, The Emperor's New Groove, Kronk's New Groove, the Mickey Mouse films, A Goofy Movie, An Extremely Goofy Movie, Space Jam, and Looney Tunes: Back in Action.
- Yru17 originally planned to re-edit this film as well as a separate Land Before Time crossover with The Sandlot, but he retired from re-editing anymore crossovers, so Yakko Warner will make this film with not only the same guest stars as originally planned, but also with Littlefoot and his friends as additional guest stars instead.
- The storyline continues in Winnie the Pooh Goes to The Sandlot 2 and Winnie the Pooh Goes to The Sandlot: Heading Home.