Major League Baseball made its rule changes for the 2020 season official on Wednesday. 

There are four categories of rules going into effect: the three-batter minimum for pitchers, roster limits, adjustments to the injured list and option periods for pitchers and two-way players, and a reduction in the time managers have to challenge a play. All but one of these changes -- the one addressing manager challenges -- had been publicly reported prior to Wednesday, but now they are all locked in.

Here's a breakdown of each rule change.

THREE-BATTER MINIMUM:
This is the big one that's been grabbing the headlines since it was first reported. 

All pitchers -- both starters and relievers -- now have to face at least three batters (or pitch until the inning is over) before they come out of a game. The only exception is an injury or illness that prevents the pitcher from being able to finish his three batters.

The main effect of this rule will be on specialist relievers, who are often used for only one batter to give their team a favorable matchup -- for example, a left-handed pitcher who faces only left-handed hitters, whom he is most likely to get out (often nicknamed a “LOOGY,” for “left-handed one-out guy”). There will be no more of that in 2020. The rule could also impact teams that use openers -- typical relievers who start a game to match up specifically against the top of the opposing order. Now, an opener would have to face at least three batters even if he has a bad matchup in that run.

The three-batter rule goes into effect in Spring Training on March 12.

ROSTER LIMITS:
There are five parts to the roster limits rule change:

26-man rosters -- Teams' active rosters are being increased from 25 to 26 players for the regular season (through Aug. 31) and during the postseason. Teams are limited to carrying a maximum of 13 pitchers.

Smaller rosters in September -- MLB is adjusting the size of September rosters to 28 players, including a max of 14 pitchers.

Previously, when rosters expanded in September, any player on a team's 40-man roster could be added to the Major League club. And while teams usually didn’t use all 40, it was common to see 30-plus players active for a given game in the final month of the season. That often caused longer games in September with teams using a lot more relief pitchers or pinch-hitters in certain situations than they would have been able to with normal roster sizes.

Two-way player designation -- A "two-way player" -- someone who both hits and pitches -- is now an official designation. That lets them stay on the roster as a position player and pitch in games without counting toward their team's 13-pitcher pitcher limit. If you designate someone a two-way player, they have to stay that way through the end of the year.

This is for players like the Angels' Shohei Ohtani, a starting pitcher and designated hitter, and the Reds' Michael Lorenzen, who appears as a reliever and also plays the outfield. True two-way players essentially hadn't been seen in the Major Leagues since the days of Babe Ruth until Ohtani arrived from Japan in 2018.

Players have to meet certain criteria to qualify as two-way players -- in either the current MLB season or the previous one, they have to pitch at least 20 innings in the Majors and start at least 20 games as a position player or DH where they bat three or more times.

The two-way player designation for 2020 also allows players who met the requirements in 2018 to qualify this season. So Ohtani, who didn't pitch last year because of Tommy John surgery but did pitch as a rookie in '18, can still be named a two-way player for the Angels right away.

Position players pitching -- Position players are allowed to pitch only if a game goes to extra innings, or if their team is winning or losing by more than six runs. During normal circumstances in a nine-inning game, only the team's 13 designated pitchers -- or two-way players -- are allowed to pitch.

Teams were using position player pitchers more than ever before in the past couple of seasons. In 2019, more than 50 different position players pitched in at least one game, generally so teams could save their pitchers' arms if they felt a game was out of hand.

The 27th man -- What used to be the "26th man" is now a "27th man" thanks to the new 26-man roster size.

Teams used to be able to call up an extra player in special circumstances -- mainly for a doubleheader. They still can ... that player is now just the 27th on the roster, not the 26th. Teams are allowed to call up a 14th pitcher for these games.

INJURED LIST AND OPTION PERIODS:
Pitchers and two-way players are returning to a 15-day injured list. That is, once they're placed on the IL, they can't be reinstated for 15 days. 

The injured list used to be 15 days for all players until the 2017 season, when it was reduced to 10 days. Position players will still have a 10-day IL under the new rules.

Additionally, pitchers who are optioned to the Minor Leagues now have to remain there for 15 days rather than 10. The option period for position players is still 10 days.

CHALLENGE TIME:
Managers now only have 20 seconds to decide to challenge a play instead of 30. 

That shortens the amount of time they have to get information about video replays, which might allow them to figure out if they'd win a challenge before they actually challenge the play. Of the changes that were announced on Wednesday, this is the only one that hadn’t previously been reported publicly.