I havent heard this idea anywhere before. I know there alot of pitfalls and risks, but yall will indulge me....
Say Mookie Betts signed a 10 year contract today starting the 2021 season and his expiring contract is traded to a desperate team, effectively a true 100% rental. He could help another team win the WS, and then go back to Boston.
I know. Its got more holes in it than swiss cheese..... but it could work at the trade deadline if Boston is out of contention and wont win the WS.... I doubt they would want to face him in the WS.
Can a player even have contracts like that or so they automatically extend?