2. Brayan Bello
The Red Sox haven't had much success developing quality starting pitchers lately, but Bello is an exception.
Similar to Casas, the young right-hander has shown a lot of promise during his first two seasons with the Sox. Like Casas, he struggled initially but worked through it and is now regarded as a key foundational piece of Boston's core.
Bello faded down the stretch this season, but for much of the year he was one of the team's only effective and reliable starting pitchers. If you remove his first two starts of the season and his last two, he went 12-8 with a 3.39 ERA, a 4.09 FIP and a 3.3 K/BB ratio while averaging nearly 6 innings per start. That's not quite ace-material just yet, but he already looks like a strong No. 2/3 starter who can anchor a rotation.
The Dominican Republic native made notable strides last year as well, especially with his control. He lowered his walk rate from 4.2 BB/9 as a rookie in 2022 to 2.6 BB/9 last season, doing a much better job of attacking hitters in the strike zone and not being afraid to make mistakes.
Bello is only 24 and still has room to grow, especially if he can get his strikeout rate up and becomes a bit more polished. Even if he doesn't find that next gear, though, he's still worth extending this offseason to give the rotation some stability for the foreseeable future.
Extending pitchers can be risky because of their injury volatility, but Bello is worth rolling the dice on.