No. 1: Star shortstop Bobby Witt Jr. regresses
Witt could regress considerably from the player he was over the final four months of last season and still have a respectable campaign. But the Royals don't need him to be just respectable: they need him to be the star he proved in 2023 he can be.
Witt became the first Royal ever to join the 30-30 club, led the majors in triples, and shook off the concerns about plate discipline that dogged him as a rookie two years ago. Some of his 2023 numbers, such as his .276 average and .319 OBP, weren't eye-popping, but recall that his rookie struggles carried over into the first two months of the season. But once he broke out in early June, he hit .303 for the rest of the season with a .347 OBP. He also had a strong season with the glove.
Now, there's no reason to be overly concerned about Witt's 2024 prospects. Everything about him screams superstar and 2023 proved he's up to the task. But until he shows everyone last season was the real deal by replicating it in this season, there will always be a sliver of worry. If he regresses, though, things will be bad for the Royals.