Mark Baldwin, the well-known base ball pitcher, has signed with the Columbus club.
-Rock Island Argus, January 24, 1891
N.E. Young, secretary of the National Board, announces the following players who have signed contracts for the coming season with clubs in the National League...Mark Baldwin, with Columbus...
-New York Clipper, February 14, 1891
Mark Baldwin, who pitched last season for the Chicago Club, of the Players' League, and who had signed for the coming season with the Columbus Club, of the American Association, is reported as having "jumped" his contract with the latter club and signed with the Pittsburg Club, of the National League.
-New York Clipper, March 7, 1891
So, first, what we have is Mark Baldwin playing with the Columbus Association team in 1889. In 1891, he jumped to Chicago and the Players League. After that operation went under, he resigned, as we see here, with Columbus before jumping that contract to join the Pittsburgh League club. It is this final move - Baldwin jumping from Columbus of the AA to Pittsburgh of the NL - that set all of this into motion.