6. July 31, 2017 : Trading Yu Darvish for Willie Calhoun
Theoretically, this could end up being one of the best deals on this list or the not worthy of the list at all. Even though the WAR is negative, the Rangers return has yet to make any real appearances at the big league level. Calhoun, the biggest piece for Texas, is considered the number 2 prospect in their system and a top prospect in the league. Expectations are high for Calhoun once he does move to the Majors full-time either this year or next.
Darvish, at the time was the Texas Rangers ace, but had an expiring contract and Texas was not a contender. The move to send him to LA, while expected, still was hard to swallow for fans. After the end of the season, Darvish signed with the Cubs though leaving the Dodgers. With him leaving LA, it essentially means that the Rangers got a top tier prospect for a 2-month rental of Yu.
Alexy, the other notable piece Texas received, is a quality catching prospect that the Rangers can hope to develop moving forward.