Season 4, Part 1 of Attack on Titan provides a lot of insight into certain characters and their pasts, especially Zeke Yeager. Prior to this, Zeke was simply known as the intimidating Beast Titan, half-brother to Eren who hails from Marley. But Season 4 provides some much-needed information regarding Zeke's childhood that both reveals and helps to contextualize his horrible euthanization plan for Eldia, as well as signature method of attack: pitching.
Like the other Marleyan Warrior candidates, we also assumed that he earned his spot as the Beast Titan based on intelligence, skill and physical capability. But, it turns out, the real reason he inherits the Beast Titan -- and why he's so good at throwing things -- has to do with a deep, human connection to the previous holder.
Originally, Zeke wasn't a serious contender to inherit any of Marley's Shifter Titans. This changed when he met Tom Ksaver, the then-holder of the Beast Titan. Over the years, Zeke spent more and more time with Tom, often playing catch with him like a father-son duo. Zeke's home life, meanwhile, was pretty tumultuous, what with his parents being critical members of the Eldian Restorationists.
The truth was his parents, Dina and Grisha, needed him to inherit a Titan for their own political plans. So much so that when it looked like Zeke wasn't making the cut, lacking in primarily physical ability, his parents were extremely disappointed and made this clear to their son. It was no wonder Zeke sought comfort in Tom.
Tom provided a stable father figure in Zeke's life. Playing catch was something that bonded them together, despite them not having any other clear connection. Tom started to throw the ball around as a way to destress from his job, which was how he met a young Zeke in the first place. Tom immediately took an interest in the underdog and, as they continued playing catch, was the first to notice his incredible pitching ability. Hearing compliments and positive reinforcement from Tom strengthened his bond with Zeke -- a far stronger one than he shared with Grisha.
Tom soon discovered that his parents were Eldian Restorationists and convinced a worried Zeke to betray them to protect himself and his grandparents. This betrayal brought Tom and Zeke even closer together. Following Grisha and Dina being sent to Paradis, Zeke also learned of Tom's true feelings about his research and their race (Eldians), in general.
Tom confided in Zeke about his own tragic past, having married a Marleyan woman only to have her discover his Eldian heritage. Out of shame and disgust, Tom's wife killed their child and then herself. Because of this, Tom felt that Eldians suffer more than other people and that sterilizing them would solve all of their problems -- gradually ridding them, and the world, of the Titan curse, thus alleviating their suffering for good.
Zeke's relationship with Tom also helped him become the Beast Titan, as Tom made it clear that, even though Zeke had made a name for himself as the 'underdog' of the Warrior candidates, Tom preferred him to become his Titan inheritor. Zeke took the role with pride, even continuing to wear Tom's iconic glasses. It was because of their time together playing catch that Zeke was able to become the Beast Titan, and became such a terrifyingly good pitcher in Titan form.
Zeke's entire journey through Season 4 is a product of his relationship with Tom. Both his devastating ability to throw objects at enemies and his big plan for Eldia are both nods to the real caretaker in his upbringing, Tom. Their connection was the cause for change in Zeke's life to happen, allowing him to assume the role of Beast Titan and use the potential that was left untended by his own parents. Without it, who knows where Zeke would be.