Rivals follows 12-year-old Josh LeBlanc, a nearly six-foot-tall shortstop for the Syracuse Titans, a U12 (under-12) travel baseball team, as he navigates injury, jealousy, and a cheating scandal on the road to a national championship in Cooperstown, New York.
Josh wakes in a hotel room on the morning of a qualifying game against the Toledo Nighthawks, feeling both excitement and dread. His father, Gary LeBlanc, a former first-round draft pick who spent 13 years in professional baseball's minor leagues, coaches the Titans and believes great players relish rivalries, but Josh privately wishes for easy victories. At breakfast, Jaden Neidermeyer, one of Josh's best friends and a writer for the local
Post-Standard newspaper, warns him that the Nighthawks' star pitcher, Sandy Planczeck, plans to throw a beanball (an intentional pitch aimed at a batter's head) if needed to win. Josh refuses to tell his father, not wanting to look afraid.
Before the game, Josh overhears his parents arguing. His father insists that advancing to the Hall of Fame National Championship Tournament in Cooperstown would secure a five-year Nike sponsorship the family desperately needs. He vows never to burden Josh with this pressure, but Josh listens silently, and the knowledge deepens his anxiety.
The game is intense. Josh's exceptional vision, his gift for reading a ball's spin the instant it leaves the pitcher's hand, allows him to hit three home runs off Planczeck's blazing fastball. With the score tied 4–4 in the final inning, the Nighthawks coach orders an intentional walk, but Josh's father signals him to chase the pitch. Instead of throwing outside, Planczeck hurls a curveball that strikes Josh directly in the face. Josh collapses, his left eye swelling shut. He refuses to take his free base and insists on batting. Switching to left-handed since only his right eye works, he blasts a three-run homer. In the bottom of the inning, with the bases loaded, Josh makes a diving catch and fires to third base to initiate a triple play, winning the game 7–6.
At the hospital, an MRI reveals a fractured orbital bone dangerously close to the optic nerve. Dr. Cohen offers two options: let it heal naturally over five to six weeks, meaning Josh would miss the tournament, or undergo surgery to install a metal plate that would allow him to play in three weeks but leave a visible scar. Josh's mother opposes the surgery, but Josh and his father insist, and Gary authorizes the procedure.
During recovery, Jaden tells Josh about Mickey Mullen Jr., the son of Mickey Mullen, a former Boston Red Sox Hall of Famer, three-time Cy Young Award winner, and Hollywood action-movie star. Mickey Jr. plays for the LA Comets, the last team to qualify. Jaden becomes increasingly focused on the Mullen story, irritating Josh and his best friend and roommate, Benji Lido, a heavyset, wisecracking boy. Josh and Benji prank Jaden with a fake voicemail pretending to offer her an exclusive interview with Mickey Mullen. She is humiliated and deeply hurt, creating a rift between them. In the week before the tournament, Josh struggles in batting practice, flinching at every pitch, but he gradually forces his eyes open and regains his swing.
At the tournament in Cooperstown, Josh and Benji sneak into a restricted area of the Baseball Hall of Fame museum, where they encounter Mickey Jr. and get caught by security. Mickey Mullen himself intervenes, charming everyone, though he subtly dismisses Josh's ambitions by pointing him toward the runner-up trophy. Josh's jealousy flares when Mickey Jr. asks Jaden for her phone number.
On opening day, the Titans beat the Miami Barracudas when Josh steals home for the winning run. Watching the Comets play on another field, Josh notices the head umpire, Justin Seevers, calling an extremely generous strike zone in their favor. After the game, Josh follows Mickey Jr.'s limousine to a restaurant, where he spots Myron Underwood, Mickey Mullen's former bodyguard and personal assistant, slipping Seevers a bulging manila envelope.
Myron soon ambushes Josh and threatens him: If Josh speaks up, the Mullens will use their media influence to destroy Gary's reputation, painting him as a washed-up player who gave his son steroids and stole his Nike deal from his former coach. Shaken, Josh keeps quiet. When he confides in Jaden, she admits she accidentally mentioned Josh's suspicions in front of Myron, whose furious reaction confirmed the bribery. Remorseful, Jaden agrees to use her access to the Mullen entourage to help gather evidence.
The Titans keep winning. A producer from HBO arranges a round-table interview with sportscaster Bob Costas featuring Josh and Mickey Jr. In New York, Josh struggles on camera while Mickey Jr. handles the spotlight effortlessly. Near the end, Josh rallies, declaring the Titans plan to win and holding his own in a verbal sparring match.
Both teams reach the championship game. Jaden tips off Josh that Myron and Seevers are meeting at the Otesaga, a grand lakeside hotel where the Mullens are staying. Josh and Benji use a camera phone to record video of Myron handing Seevers another envelope of cash. That evening, the three friends go to Seevers's house and spot the envelope on a desk through a window. Josh climbs inside and grabs it, but Seevers catches them and fires a shotgun as they flee. They escape in a motorboat across the lake, with Seevers in pursuit. Jaden steers them to the Otesaga, where a celebrity barbecue is underway.
The motorboat runs aground on the beach before hundreds of guests. Myron seizes the envelope, but Benji squirts hot sauce in his face, causing him to drop it. Jaden snatches the envelope, grabs a microphone onstage, and announces the bribery to the crowd. Mickey Mullen quickly blames Myron, claiming his assistant acted alone. Privately, Costas tells Josh and Jaden he does not believe Mickey's story but cannot disprove it. He assures them cheaters eventually get caught.
The next day, the Titans face the Comets with a new, fair umpire. Josh's father's strategy is to wear down Mickey Jr.'s tired arm by forcing extra pitches. The Comets build a 5–2 lead, but in the final inning, Mickey Jr.'s arm begins to fade. Mickey Mullen orders his son to intentionally walk Josh. Mickey Jr. refuses, defying his father. He throws a fading fastball, and Josh crushes a three-run homer to tie the game 5–5. With two outs, Benji comes to the plate. Josh's father kneels beside him and tells Benji this is his moment. On an 0–2 count, Benji connects on a high fastball. The ball strikes the top of the right-field fence and drops back into play. Benji rounds the bases but must sprint the final stretch when the outfielder throws home. He lowers his shoulder and plows through the catcher, knocking the ball loose. The umpire calls him safe, giving the Titans a 6–5 walk-off victory.
A helicopter lands on the outfield. Mickey Mullen drags his son toward it, but Mickey Jr. breaks free to find Josh. He tells Josh that next time the result will be different. As the helicopter shrinks into the sky, Josh admits to Jaden he is genuinely looking forward to facing Mickey Jr. again. Jaden reminds him this is exactly what his father always said he needed to become great: a true rival.