Happy Gilmore (Adam Sandler) is an aspiring ice hockey player who possesses a powerful and dangerous slapshot that his father (Louis O'Donoghue) taught him as a child (Donnie MacMillan) before he was apparently struck and killed by a wayward hockey puck, though his over aggressive streak (which once resulted in him trying to stab a guy to death with an ice skate) and lack of skating talent consistently preclude him from joining a hockey team. His girlfriend Terry (Nancy McClure), a schoolteacher, leaves him because of his hockey obsession.
His grandmother (Frances Bay) has not paid her taxes for many years. As such, she owes the IRS $270,000 in back taxes, and the house is about to be seized. Gilmore has only 90 days to come up with the money or else the house will be auctioned off. Grandma Gilmore is forced to temporarily move into a retirement home, run by a sadistic manager named Hal (Ben Stiller in an uncredited role). While repossessing Grandma's furniture, a pair of movers challenge Happy to hit golf balls. With his unorthodox, hockey slapshot-style swing, Happy hits the ball 400 yards three times, winning $40 as a result and starts hustling golfers with his swing at the driving range, leading former golf star and current club pro Chubbs Peterson (Carl Weathers) to convince Happy to enter a local tournament for a chance to win "big bucks". Peterson is known for losing his right hand to an alligator during his career. Happy wins the tournament and earns a spot on the Pro Golf Tour, though Chubbs advises him to wait 6 months so he can improve Happy's performance.
On the tour, Happy encounters Shooter McGavin (Christopher McDonald), who sees Happy as both a detriment to golf and a threat to his career. Although Happy has a powerful drive, his putting is terrible with violent outbursts and lack of golf etiquette. Commissioner Doug Thompson (Dennis Dugan) demands to expel him from the tour, but PR head Virginia Venit (Julie Bowen) convinces him to reconsider, citing higher television ratings, increasing attendance, drawing more youthful sponsors, and that she's willing to work with Gilmore on his anger issues. Thompson threatens to fire her as well if there are any further incidents; Happy begins to improve his performance and behavior and becomes an instant celebrity.
Then during a pro-am tournament with then-host of The Price Is Right Bob Barker, he gets distracted by an insulting fan named Donald (Flaherty), causing Barker and Happy to lose the tournament and Barker and Happy get into a brawl. Barker wins the brawl, but it's revealed that Shooter hired Donald to distract Happy and get him kicked off the tour. Thompson has a meeting with Happy, Virginia, and Shooter about the brawl with Barker, and Happy tries to tell Thompson about Donald bothering him and that Happy wanted to attack Donald and not Barker. Thompson says that due to the high TV ratings of the tournament, he decides not to kick Happy off the tour, but Happy is still punished with a one-month suspension and a $25,000 fine. Happy tries to tell Thompson about Grandma's house but is sent away by an angry Thompson.
While being suspended, Happy becomes a spokesperson for Subway and gets enough money to get Grandma's house back, but when he gets to the house, an auction takes place and Happy is outbid by Shooter who has purchased the house for $350,000. Happy makes a bet with his rival based on the upcoming Tour Championship. He seeks the help of Chubbs, admitting his past mistakes and the two head to a miniature golf course. Happy progresses with Chubbs teaching him to go to his 'happy place' when he cannot calm down.
That night, Happy takes Chubbs back to his house to thank him for helping. Chubbs gives Happy one of his prized irons as an improvement gift, and Happy tells Chubbs that he has a gift for him too. Chubbs opens a large box, which has the present in it; the head of the alligator that took his hand, which Happy killed during one of his golf tournaments. Seeing the creature, Chubbs screams and falls backwards out of a window to his death.
Determined to win the tournament for Chubbs, Happy is evenly matched with Shooter after the first two rounds and leads Shooter by the end of the third day. On the fourth and final day, multiple unusual scenarios occur between both Happy and Shooter, with the latter losing after the former succeeds in the trick shot learned from Chubbs. Afterwards, an angry and hysterical Shooter attempts to steal Happy's gold jacket, but is chased down by Mr. Larson and an angry mob of spectators. Back at Grandma's house, the film closes with Happy being congratulated by the two-handed ghost of Chubbs, Abraham Lincoln, and the alligator.
What does Chubbs give Happy as an improvement gift?
One of his prized irons