Stand Up was the 21st episode of Season 4 of Quantum Leap, also the 74th overall series episode. Written by Bill Richmond and Deborah Pratt, the episode, which was directed by Michael Zinberg, made its world premiere on NBC-TV on May 13, 1992.
April 30, 1959: Sam leaps into a man named David "Davey" Parker (leapee played by Rafe Battiste) who's part of a comedy act with his male partner Mack MacKay (Bob Saget); they are regular headliners at a resort and nightclub in the Poconos in the late 1950s. Newly hired female partner Frankie Washarskie (Amy Yasbeck), who works at the resort as a waitress, and who also often accompanies them on stage to perform, wants desperately to be a regular part of the act, making it a trio, to Mack's stubbornly adamant and bitter demand.
As Davey, Sam, who leaped into him as the three were performing, realizes Frankie's comedic timing, also realizing that her talents are needed in what was a dying act without her, (one of Mack's stale jokes was a one-line insult where he asks Davey "What are you, comedically stunted, or hopelessly stupid!?) as she helped the act to get a grand applause at the show's end that night, as well as good reviews in the local newspapers.
Sam, with the report of Ziggy, through Al, and with Al's agreement, also realizes that his mission is not only to convice the stubbron Mack to relent on his refusal to allow Frankie, who he's been dating, to not only join the act, but to get the two, who are constantly arguing due to Mack's control issues, to see that they love each other, and prevent one of the comedians from getting "knocked off" by the Mafia.
One big problem in Sam accomplishing his mission, is that, the quick-tempered Mack who's also a control freak, has had a history of changing up the act in the past several years, as Davey, Sam's leapee, seems to have been the "voice of reason" that could possibly get his stubbron, controlling Mack, who's had a series of fallouts with his previous comedic partners in the past four years, to listen to suggestions to improve the act.
Not only dose Sam get him to grudgingly relent and allow Frankie a chance as the act's 3rd wheel, but also manages the club's manager Lou Collins (Mark Lonow). to relent and change his mind, after the hot-headed Mack managed to get the act fired from their gig at the club after getting into it with him after he calls Lou's club a "two-bit flea bag hotel".
All of their lives get a little more complicated when notorious local area mobster Carlo Degorio (Robert Miranda) offers them a contract to perform at his club in Las Vegas. They're thrilled at the opportunity, but it's also obvious that the gangster's real interest is in Frankie. When Al tells Sam that Mack will "disappear" that night he has to be quick on his feet to get the mobster to lay off.
At the end of S04E01 "The Leap Back" Al says that Sam leaped into a stand-up comic (playing the Catskills) in 1956, where he's meant to save a little girl that's being torn apart by a divorce, and make sure that she has a good stable home to be raised in. Though we never see that leap ourselves, in this episode (S04E21 "Stand Up") Sam is a stand-up comic in1959. He has a completely different goal in this leap, but the vague resemblance between the two leaps is interesting.