Spoiler alert for Game of Thrones season 6, episode 9, "Battle of the Bastards." Duh.
The "Battle of the Bastards" is the episode of Game of Thrones no one can stop talking about (so, basically just like every other episode of Game of Thrones). Today's topic is: "Where was Jon Snow's direwolf, Ghost, during the battle?" The answer: doggy daycare. Kidding! The real answer is that Snow chose not to bring him along, on purpose. And apparently Ghost is such a wusswolf he just does whatever Snow says. Pssht.
Liam Cunningham, who plays "Onion Knight" Davos Seaworth on the show, told Tech Insider: "I would prefer to have Ghost with Davos [rather] than with Jon. Even though it's his direwolf, I just like the idea of an insurance policy." He added,
Yeah that [having Ghost in the battle] would have been cool, [but] obviously a big battle like that is no place for a direwolf. They're not gonna last very long—I mean look at what happened to Wun Wun, the last of the giants.
(Oops, spoiler: RIP Wun Wun.)
In an interview with Business Insider, Miguel Sapochnik, the episode's director, explained what is perhaps the more pragmatic answer:
[Ghost] was in there in spades originally, but it's also an incredibly time consuming and expensive character to bring to life. Ultimately we had to choose between Wun-Wun and the direwolf, so the dog bit the dust.
Thankfully, what Sapochnik really means is: Wun Wun bit the dust and Ghost is fine. Unlike all the other direwolves, who are all dead (right, except maybe Arya's?) because Game of Thrones LOVES killing animals (almost as much as it loves killing people).
"HOW MANY THINGS CAN WE KILL IN THIS EPISODE?" is probably how every writers' room meeting starts, after said writers have finished drinking mugs of kitten blood. But not Ghost, not yet. He's still under contract. Probably chilling in a CGI green room somewhere, eating stale Cheez-its.