Canceled TBBT storyline fans never got to see because of Kaley Cuoco's accident
In fall 2010, Zack was supposed to teach Sheldon Cooper how to talk to women. Then Kaley Cuoco's horse threw her, and the episode went with her. The man who played Zack says that's for the best.
Brian Thomas Smith, who played Penny's sweet, spectacularly dim ex Zack Johnson, sat down with host Jessica Radloff on The Official Big Bang Theory Podcast for an August episode titled "Zack, The Justice League, and the Lost Episode." The lost episode is the one Zack was supposed to anchor early in season 4, and Smith described its premise in one line:
"I was giving Sheldon advice on women in that episode."
— Brian Thomas Smith, on The Official Big Bang Theory Podcast
They'd had a few days of rehearsal. Then Smith got a call on a Sunday night: Cuoco had been hurt in a riding accident, and since Zack's whole storyline ran through Penny, there was no episode without her. The production told him plainly: "She can't do the episode, so you're not going to be able to do the episode." His reaction, by his own account: "This is my luck."
The accident behind it
The injury was much worse than a scheduling problem. In September 2010, Cuoco was riding at a ranch outside Los Angeles when the horse threw her and stepped on her left leg. Chuck Lorre told Radloff, for her 2022 oral history of the show, that it was the scariest stretch of the entire run:
"That was the darkest, most frightening time in all twelve years. Kaley could have lost her leg."
— Chuck Lorre
Cuoco has since said she still has pins and rods in that leg. She missed two season 4 episodes, the only main cast member ever to miss two. For weeks after that, Penny worked behind the Cheesecake Factory bar so the camera never saw the boot.
Why Smith is fine with it
Here's the part that makes the lost episode less of a loss. Smith doesn't remember it fondly. Asked about it, he was blunt: "it wasn't good." Zack in that script, he said, was "kind of mean, still," written as "more like a womanizer type of guy," and he was "glad it was a little softer" in the episodes that actually aired.
That softer Zack is the one fans love: the guy who wasn't smart enough to notice he was being mocked, and too good-natured to mind when he did. A version of Zack coaching Sheldon on picking up women would have built the character on the opposite trait.
The episode was scrapped because of an injury that nearly cost Kaley Cuoco her leg. The actor at its center says the script wasn't good.
Bill Prady called Smith afterward to say they wanted him back, and Zack returned that December in two straight episodes: "The Alien Parasite Hypothesis," where Amy gets a crush on him, and "The Justice League Recombination," where he joins the guys' costume team for New Year's Eve. Smith suspects the costume contest started out as a Halloween episode and got pushed because of him. Justice League is now one of the show's best-loved half-hours. Alien Parasite is the one its own future showrunner calls his least favorite of all 279.
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Zack ended up in 11 episodes. This summer, Smith played him again in a surprise cameo on the new spinoff Stuart Fails to Save the Universe, opposite Cuoco, with her leg fully intact and nobody hiding her behind a bar.
Previously we wrote: Who is Ariana Grande playing in Focker In-Law? Ben Stiller's character is convinced she's "trained to manipulate people"