二刀流球員定義
MLB teams must designate every player on the active roster either as a pitcher o
r a position player and are limited to carrying 13 pitchers on the active roster
(14 pitchers from Sept. 1 through the end of the regular season).
大聯盟球隊必須指定名單中每一個球員是投手或野手，名單中最多只能帶13名投手。（9/1
以後到賽季結束時增加為14名）
Those designated as position players are unable to pitch unless it is extra inni
ngs or their team is ahead or trailing by more than six runs when they take the
mound. Teams can also designate players as two-way players if they meet certai
n criteria. Two-way players are able to pitch in any situation but don't count t
oward the active roster's pitcher total.
擔任野手的球員不能上場投球，除非是延長賽或者登板時已經落後/領先超過6分。球隊也能
指名
達成特定標準的球員為二刀流，二刀流可以在任何情況上場投球，但不佔投手的名額。
Players qualify for the two-way designation if they have met both of these condi
tions in either the current or previous MLB season:
於當前或者是前一個球季同時達成下述兩項標準的球員可以被指名為二刀流
‧ Pitched at least 20 Major League innings
‧ Played at least 20 Major League games as a position player or designated hitt
er, with at least three plate appearances in each game
在大聯盟投至少20局
在大聯盟以野手或指定打擊身份出賽至少20場，且每場最少要打3打席
來源：https://www.mlb.com/glossary/rules/two-way-players
大概是這樣
有二刀流在球隊調度會比較有彈性，可是要怎麼取得資格感覺會是很大的問題XD