Ross only pitched in 12 games — 10 starts — this year for Texas, posting an ugly 7.71 ERA and a K/BB ratio of 36/37 in 49 innings. He only pitched in one game for the Padres last year as a result of thoracic outlet syndrome. He recovered from that, physically speaking, but his pitching has not rebounded. It’s an open question as to whether he’ll pitch again, actually, and he’ll certainly do no better than a minor league invite next spring.
Jay, 32, hit .296/.374/.375 in 433 plate appearances with the Cubs last season, which is adequate. He’s heralded more for his defense and his ability to play all three outfield spots.
The Mariners are losing center fielder Jarrod Dyson to free agency and likely don’t want to rely on Guillermo Heredia next season, hence the interest in Jay. The free agent class for center fielders is otherwise relatively weak.