With two-way players now a part of modern baseball, and potentially a wave of the sport's future, Major League Baseball has introduced a rule to govern their usage. A new "Two-Way Player" designation was among the rule changes the league and Players Association announced Thursday. It will go into effect

With two-way players now a part of modern baseball, and potentially a wave of the sport's future, Major League Baseball has introduced a rule to govern their usage.

A new "Two-Way Player" designation was among the rule changes the league and Players Association announced Thursday. It will go into effect in 2020 as part of a set of criteria determining how clubs can use their players in the regular season and postseason.

This change is seemingly designed to curb the use of position players as pitchers, which has become quite common in recent years: In 2018, there were 48 instances of position players pitching (not including Shohei Ohtani), an all-time high. That was more than double the 23 instances in '17, which was the previous record.

With that as the backdrop, here is everything else you need to know about this change.

What's the rule?

In general, every player on a team's active roster will have to be designated as a pitcher or a position player. That designation must stay the same for the entire season. And starting in 2020, the number of pitchers a club can carry on the active roster will be capped, with the exact number to be determined.

Only players designated as pitchers will be allowed to pitch in a game, including in the postseason, with three exceptions.

1) The game goes into extra innings.

2) A team is winning or losing by six or more runs.

3) The player has earned “two-way” designation.

So how does a pitcher get two-way player status?

A player qualifies for two-way status if he:

1) Pitches at least 20 Major League innings AND

2) Plays at least 20 Major League games as a position player or designated hitter, with at least three plate appearances in each game in either the current or previous MLB season.

Once a player has earned the two-way player designation, he maintains that status for the rest of that season and the following season. And while he has that status, his team no longer has to use one of its pitching roster spots on him.

Long story short: A two-way player is basically a position player who is allowed to pitch with no restrictions.

How does this affect Ohtani?

Shohei Ohtani is currently the only true two-way player at the Major League level. He's also the only player who would qualify for two-way status if the rule went into effect this year as opposed to next.

But here's the thing -- Ohtani won't be pitching at all this season as he recovers from Tommy John surgery. So he'll have to re-earn his two-way player designation in 2020, when the new rule is implemented.

Essentially, if the Angels plan on Ohtani hitting and pitching in the 2020 season, they'll have to designate him as a pitcher. There's no restriction on players who've been designated pitchers as far as letting them bat -- it's only players carrying a position player designation who cannot also pitch.

The Angels should be able to designate Ohtani as a pitcher for 2020, then continue to also use him as a DH like they did in his rookie season. Once he reaches the 20 innings pitched and 20 batting games thresholds, he'll immediately qualify as a two-way player under the rule for the rest of '20 and all of '21. At that point, the Angels would potentially gain an extra “pitcher” spot on their roster.

So while you can’t switch from pitcher to position player during the season, you can switch from pitcher to two-way player during the season once you have met the necessary benchmark.

How does it affect two-way converters?

Matt Davidson was one of the most frequent position-player pitchers last season, and the most successful. Now he's trying to make it as a two-way player with the Rangers. He basically has the 2019 season to prove he's for real.

If Davidson sticks as a two-way player, he can use this year to preemptively earn two-way status for 2020. But if he doesn't meet the innings pitched and batting games requirements, his team would be a lot more constrained in 2020.

Let's say Davidson doesn't reach 20 innings and 20 batting games this season. If a team then wanted to use him on the mound and at the plate in 2020, it would have to designate him as a pitcher for the season -- because if he were designated as a hitter, he wouldn't be allowed to pitch in any game that wasn’t a big blowout or didn’t go into extra innings.

But that would clog up one of the limited active roster spots available for pitchers. With the number of pitcher slots capped starting next year, carrying a two-way convert who's not as effective or experienced as a normal pitcher probably wouldn't be worth it.

The same goes for any other position players attempting the same two-way conversion. Any teams that want to try out someone as a two-way player need to get in those innings and batting games now, in 2019, when their roster usage isn't yet restricted.

But keep this in mind: You don’t get to keep your two-way status for life. If you earn the status in one year you get to keep it for the rest of that season and the next, but not in perpetuity. If you don’t reach the thresholds in a given season, you’ll lose that two-way designation and have to exceed the benchmarks again the following year.

How does it affect future two-way prospects?

The other key remaining category is two-way players in Minor League pipelines. The biggest name there is Brendan McKay, a left-handed pitcher and DH/first baseman who's a true two-way prospect, ranked No. 3 in the Rays organization and No. 29 overall in baseball.

McKay, naturally, won't have met any of the two-way player criteria when he reaches the Majors. That will put him in the same boat as the one Ohtani is in for 2020.

Assuming the Rays still want to use McKay as a two-way player once he gets to the big leagues, they'd probably also designate him as a pitcher, while also allowing him to bat. Once he pitched 20 innings and hit for 20 games (with three plate appearances in each), McKay would immediately qualify to become a two-way player for that season, opening up another “pitcher” spot on the roster.

David Adler is a reporter for MLB.com based in New York. Follow him on Twitter at @_dadler.