Paul Goldschmidt has been traded from the Arizona Diamondbacks to the St. Louis Cardinals for catcher Carson Kelly, pitcher Luke Weaver, infielder Andy Young, and the Cards competitive balance pick for 2019. Goldschmidt, one of the best first basemen (and, for that matter, one of the best players) in baseball, is in the final year of his deal, and is a free agent after 2019.
The Cardinals now have a huge upgrade for their lineup, and can plug Goldschmidt in at first base, where Matt Carpenter and the defensively-challenged Jose Martinez split time in 2019. I would have thought the D-Backs would have sought Martinez in a deal for Goldschmidt, but instead, Martinez stays in St. Louis for now.
As for the D-Backs, they get a couple of guys in Kelly and Weaver who are well regarded, but who regressed some in 2018. The 24 year old Kelly gets great marks for his glove, but has a 415 OPS in 131 major league plate appearances, and saw his OPS at AAA last year drop by 61 points. Weaver, 25, followed up a solid 2017 whee he had a 3.88 ERA in 60 major league innings with a 4.95 ERA and -1.1 bWAR in 2018, leading to questions about whether he will stick in the rotation. Young, 24, was a 37th round pick in 2016 who had a breakout year in 2018 between high-A and AA.