One of Major League Baseball's biggest winter deadlines passed on Friday evening. Teams had until 6 p.m. ET to place their Rule 5-eligible prospects on their 40-player rosters in order to prevent them from being included in the draft pool. 

For those unaware of the Rule 5 Draft's existence or its function, it's essentially a mechanism that protects against talent-hoarding. Individuals who signed when they were at most 18 years old must be placed on the 40-player roster within five draft cycles, while individuals who signed when they were at least 19 years old have just four cycles. In the past, players like Roberto Clemente, Johan Santana, and -- most recently -- Akil Baddoo have changed teams as part of the Rule 5 Draft process.

It should be noted that this year's Rule 5 Draft could be delayed or otherwise interrupted if the owners lock out the players following the expiration of the current Collective Bargaining Agreement. Nevertheless, we here at CBS Sports have chosen to highlight 10 notable prospects whose teams opted to protect them ahead of Friday's deadline. The players are presented below in alphabetical order.

1. Nick Allen, SS, Athletics

Allen, part of the United States Tokyo Olympic Team, is one of the top defensive shortstops in the minors. The reason he isn't a better known prospect nationally has to do with the uncertainty surrounding his offense. He reached Triple-A last season, hitting just .243/.302/.301 in a 39-game stint; for reference, that particular A's affiliate hit .277/.355/.481 as a team. Provided Allen's bat shows more life in his first full-season run at Triple-A, he should end the year as Oakland's starting shortstop. 

2. Jeter Downs, INF, Red Sox

Hailed as the key piece of the Mookie Betts trade return, Downs had a miserable first crack at Triple-A. In 99 contests, he batted .190/.272/.333 with an elevated strikeout rate (all the way up from 18 percent to 32 percent) and a reduced ISO. If Downs can return to his typical well-rounded former next season, he should be able to make his Boston debut. Another poor showing, however, and his stock will crater.

3. MacKenzie Gore, LHP, Padres

As with Downs, Gore's standing is trending in the wrong direction. He appeared in 12 games across various levels in 2021, accumulating a 3.93 ERA despite walking five batters per nine innings. He's made three appearances in the Arizona Fall League, during which he's issued six free passes in 11 innings. Until Gore regains his command (ahem, if he can regain his command, even) it's hard to view him as starting material -- that's a fall from someone who once elicited comparisons to Clayton Kershaw based on his mechanics and his knee-buckling curveball.

4. Hunter Greene, RHP, Reds

Greene, the No. 2 pick in the 2017 draft, fared well in his return to game action after missing time because of Tommy John surgery and the pandemic. In 21 starts across two levels, he posted a 3.30 ERA and a 3.56 strikeout-to-walk ratio. Greene still possesses elite arm strength. If he can shore up his secondary offerings and his command, he ought to make his big-league debut sometime during the 2022 season. 

5. DL Hall, LHP, Orioles

It's easy for Orioles prospects to get overshadowed by the likes of Adley Rutschman and Grayson Rodriguez. It doesn't help Hall's exposure that he was limited to just seven appearances last season because of elbow woes. When he's hearty and hale, he has high-quality stuff; it's to be determined if his command allows him to start.

6. Royce Lewis, SS, Twins

Lewis, who was the top pick in that 2017 class, can only hope to follow in Greene's footsteps after tearing his ACL in spring. While there's never an opportune moment to miss an entire season, Lewis' misfortune came at a particularly poor time, as he had scuffled through the 2019 campaign. Development is seldom linear; the Twins hope that Lewis can prove as much by putting the past few years behind him, and quickly.

7 & 8. MJ Melendez, C; Nick Pratto, 1B, Royals

We're pairing the two Royals because they each authored an impressive turnaround story in 2021 after having miserable 2019 campaigns. Melendez hit .288/.386/.625  with 41 home runs while Pratto batted .265/.385/.602 with 36 home runs. Each is likely to make their big-league debut and factor into a new-look Royals lineup before long -- who knows, maybe one of them even cracks the Opening Day roster. 

9. Jeremy Peña, SS, Astros

Peña is the closest thing the Astros have to an heir apparent to free agent Carlos Correa. He was limited to just 37 games last season because of a wrist injury. In those outings (primarily played at the Triple-A level), he hit .297/.363/.579 with 10 home runs and six stolen bases (on seven tries). Peña's 41-to-8 strikeout-to-walk ratio suggests he could use additional seasoning, but there's a good chance he makes his big-league debut in 2022 as Houston's next long-term starting shortstop. 

10. Julio Rodríguez, OF, Mariners

Rodríguez, 20, is one of the top prospects in the minors. He split last season between High- and Double-A, batting .347/.441/.560 with 13 home runs and 21 steals over 74 games. (Rodríguez missed some time partaking in the Tokyo Olympic Games.) He's certain to start next season in the minors, but once he arrives in the majors over the summer he has the kind of classic right-field profile that should allow him to carve out a lengthy career as a run-producing, middle-of-the-order hitter.