The Natural

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Roy Hobbs is a boy who is a skilled baseball player, often playing catch with his father Ed (Alan Fudge). One day, his father suffers a fatal heart attack and drops dead near a tree on the family property. When the same tree is later struck by lightning, Hobbs fashions the heart of the tree's trunk into a bat, which he dubs "Wonderboy", carving a lightning bolt into it.
In 1923, a 19-year-old Hobbs (Robert Redford) is a promising pitcher. He informs his girlfriend, Iris (Glenn Close), that he has been asked to try-out with the Chicago Cubs, which they celebrate by spending the night together. On the way to Chicago with his manager Sam Simpson (John Finnegan), the train stops at a carnival and Hobbs is challenged to strike out "The Whammer" (Joe Don Baker), the top hitter in the Majors. Hobbs proceeds to do so. Sportswriter Max Mercy (Robert Duvall), travelling with Whammer, acts as the umpire and later draws a cartoon of the event.
Hobbs also encounters Harriet Bird (Barbara Hershey) on the train. A mysterious and alluring woman, Harriet becomes fixated on Roy after he strikes out Whammer. Hobbs spends the evening with her drinking and discussing Roy's plans to be the best baseball player ever. After reaching Chicago, Bird lures Hobbs to her hotel room, asks him if he will be the 'best that ever was', to which he replies yes. She shoots him in the abdomen, and then jumps from the hotel window. It is later revealed that Bird, a serial killer, kills rising athletes with a silver bullet. Hobbs' wounds puts an apparent end to his promising baseball career.
Sixteen years later, a 35-year-old Hobbs re-emerges and is signed to the New York Knights as a hard-hitting right fielder, much to the ire of the team's manager and co-owner Pop Fisher (Wilford Brimley). Pop is angered over being saddled with a "middle-aged" rookie and does not play him, or even let him practice with the team. After the team's slump continues for several weeks, Pop finally allows Hobbs to take batting practice. There, Hobbs shows his hitting ability, hitting every pitch into the Knights Field stands.
During the next game, the team's star player, right fielder "Bump" Bailey (Michael Madsen) angers Pop. Pop sends Hobbs in to pinch hit for Bump, telling him to "knock the cover off the ball". Hobbs literally does just that, winning the game just as lightning strikes in the sky above the stadium. The next day, Iris, living in Chicago, learns of Roy's rise to prominence from a movie newsreel. Now sharing the spotlight with the team's newest star, a galvanized Bump dies after crashing through an outfield fence. Hobbs then becomes the league's sensation by turning the Knights' fortunes around.
Hobbs is summoned to a meeting with the principal owner of the team, the Judge (Robert Prosky), who has an agreement with Pop that if the Knights fail to win the pennant at the end of the season, Pop's share of the team reverts to the Judge. If they win, Pop can buy his and the Judge's shares back. To ensure the team loses, the Judge had the team's roster stocked with unknown players like Hobbs. When Hobbs refuses a bribe to throw the season, gambler Gus Sands (Darren McGavin) and the Judge plan to manipulate him though Memo Paris (Kim Basinger), a mesmerising blonde who is Pop's niece, and was also Bump's girlfriend until his death.
At practice, Hobbs displays the talent that once made him an incredible pitching prospect, to the surprise of his teammates. Mercy witnesses this, and finally remembers meeting Hobbs years earlier. Mercy reveals his discovery to Hobbs, and also introduces Hobbs to Gus and Memo. Hobbs begins a relationship with Memo and soon falls into a slump, despite Pop's warnings that Memo is "bad luck".
In Chicago, Hobbs comes to bat having already struck out twice in the game. During his third at-bat, Iris stands in the crowd, attracting Hobbs' attention. Hobbs promptly hits the game-winning home run, shattering the scoreboard clock. Hobbs meets Iris after the game and they reminisce. He pleads for her to come to the next day's game, but she is noncommittal. The press dubs Iris "The Lady in White" and lands her picture on the front page of the paper along with Hobbs, prompting panic from Gus and Memo. After the game the following day, Iris is waiting. Hobbs confides to her about the shooting and how he lost his way in life. In her apartment, Hobbs sees a glove and ball, and Iris reveals that she has a son whose father lives in New York.
With Hobbs hitting again, the Knights surge into first place, needing just one more win to clinch the pennant. Hobbs again refuses a payoff from Gus. During a party at Memo's apartment, she feeds him tainted food which causes him to collapse and be rushed to the hospital. When he awakens, the Knights have lost their last three games, forcing them to a one-game playoff against the Pittsburgh Pirates. The doctor informs him that the silver bullet from the shooting has been eating away the lining of his stomach, which could burst at any time and kill him instantly. Memo visits and tries to convince him to miss the game, accept Gus's offer, and run away with her. The Judge visits as well and offers Hobbs $20,000 to throw the game. Hobbs declines, and the Judge attempts to blackmail him with crime scene photos of the shooting. The Judge also reveals that he has paid off another player, and that no matter what Hobbs does, the Knights will lose.
Before the playoff game, Hobbs visits the Judge in his office to return the bribe, much to the Judge's disbelief. In anger, Memo fires the Judge's gun at Hobbs' feet, while revealing that she hates him.
After realizing the Knights' starting pitcher is the player the Judge has bribed, Hobbs confronts him on the mound, telling him not to throw the game. Iris, in the stands with her son, asks an usher to deliver a note to Hobbs. It finally conveys what Iris has been struggling to tell Hobbs since they reconnected: that her son is his from the night they spent together. Hobbs reads the notes and is shocked by this revelation.
The Knights trail 2â0 in the bottom of the 9th and Hobbs comes up to bat with two outs and runners on first and third. After opening with two balls, the Pirates bring in a young left-handed pitcher who, like Hobbs had been in his youth, is a highly touted prospect with a blazing fastball. Down to his last strike and with lightning striking in the distance, Hobbs hits a foul ball that splinters Wonderboy. Hobbs turns to the bat boy and asks him to "pick him out a winner". He returns with the bat that Hobbs helped him make. Hobbs proceeds to hit the next pitch into the lights on top of the right field stands, winning the game and the pennant. As he runs the bases under the showering lights, his team rejoices.
Some time later, Hobbs plays catch with his son on Iris' farm, as she looks on.

Question: who  reveals his discovery to Hobbs?
Answer: Mercy; Mercy