NIKON D750, D610, D800.
EOS R. SONY A7 III, NIKON Z 6.
Eos 5D- III, EOS 5D-IV.
For baseball infield shots I think a full frame offers a lot more lens options. For the Outfield in baseball a 400 to 600 millimeter lens on a crop frame is useful, but when you are stationed along the third base or first base lines, I think a 70 to 300 and a full frame offers a good combination. I used to shoot High School, Legion, AAU, and minor-league baseball with a 1.5 x Nikon D2x, and a 100 to 300 mm F4 Sigma HSM was my favorite lens. The D2x offered 1.5x at 5 frames a second, and in its HSC or high-speed crop mode, it gave 8.2 frames per second at 6.7 megapixels, which greatly boosted the utility of telephoto zoom lenses when shooting from fixed positions.
The last baseball I shot was a college tripleheader. I used a Nikon D3x full frame and a Nikon 300 mm f 2.8 AFS-II. It was a really good combo and on the few outfield fly balls I was able to crop away about 50% from the 24-megapixel original raw file and I still had pretty good quality, mainly because the Nikon 300 2.8 is such a great lens.