Mariners SS - 2000 Álex Rodríguez
Despite a rather unsavory departure from the team and tainted reputation from links to steroid use, A-Rod, in seven years in Seattle, finished top-three in MVP voting twice and was already worth 38.1 WAR through the age of 24.
If the team had his talent during the ‘01 season, the hypothetical win total is insurmountable, but alas, that is not the case. Still, he did have the single-greatest season for a Mariner playing shortstop.
His second-place MVP finish in 1996 with a league-leading .358 batting average and 36 HR comes to mind first. It is not the season that was his best. Neither is his 42 HR-46 Stolen Base 1998 season.
Ranking as his best is the only season of his career. He was worth over 10.0 WAR, his 10.4 WAR ‘00 season.
Being the best defensive season of his career (2.4 dWAR), as well as one of, if not arguably his best, offensive seasons, it was a relative no-brainer to pick.
Hitting 41 HR and driving in 132 runs, he had a 1.026 OPS and Mariners’ career-high 163 OPS+. One of the biggest reasons it was his best season was his ability to get on base by any means. His 100 walks were the most of his career, and was 41 more times than in his ‘96 season and 55 more than in 1998.
Walking at a much higher rate led to a .420 on-base percentage, the best of his time at Seattle and the third-best of his career.
Although he only had 15 stolen bases, it was the most all-around year of his time in Seattle, and his defensive ability being much better in 2000 than the other two great offensive years makes the decision to pick ‘00 easy.