Keller worked on adjusting his curveball during the offseason, Anne Rogers of MLB.com reports.
Keller is competing for a rotation spot this spring. He's needed to make some improvements after posting ERAs of 5.39 and 5.09 over the last two seasons. He ended 2022 in a relief role, and the competition from veterans and prospects alike makes a return to a starting role challenging. Keller hasn't often used a curveball before, but adding one to his repertoire could give him a new look to test hitters as he tries to produce a bounce-back campaign.