Erik Hanson: 1990 w/5.0 WAR
Matt Young: 1983 w/5.1 WAR
Dave Fleming: 1992 w/5.1 WAR
Jim Beattie: 1984 w/5.1 WAR
Mike Parrott: 1979 w/ 5.2 WAR
The Mariners had a handful of guys throughout their first 25 seasons put together great years while pitching. Each of them only did it once, and barely made it to the 5.0 WAR threshold.
Jim Beattie came over to the Mariners from the Yankees in 1980 and was a pretty solid pitcher for the Mariners. He never seemed to match up great numbers with a lot of innings, until 1984. He threw 12 complete games that season, eclipsing 200 innings for the first time in his career. He had a 3.41 ERA, but 3.2 BB/9, and it would be his last full season pitching.
Then we get to a run of Mariners who pitched their best season early in their careers. Both Dave Fleming and Matt Young did it while they were Rookies. Fleming would finish third in ROY voting in 1992, throwing 228.1 innings, with four shutouts. He hardly struck anyone out, with just 112 K’s.
Matt Young actually made the All-Star game his Rookie Year but didn’t receive any votes for Rookie of the Year (robbery!), even though he had a full WAR higher than anyone who did get a vote. He finished with an ERA of 3.27 through 203.2 innings, with a 131 ERA+. It was a very impressive season for Young, but he would never throw a season above a 2.0 WAR again.
Erik Hanson had thrown a bit for the Mariners, but 1990 was his breakout year. He finished with a 3.24 era in 236 innings, and more impressively, a 2.74 FIP. He’d also finish with a career-high 211 strikeouts, nearly 50 more than he would ever have again in a season. Go check out the Cy Young voting, and you can see how far voters have progressed since then. Roger Clemons had a 10.4 WAR and lost out to someone with a 2.9, all because the guy had 27 wins.
The one that comes in at #8 belongs to Mike Parrott. He threw 13 Complete Games, 229.1 innings, and actually threw a bit out of the pen as well, with eight games as a reliever. His season may not look better than Matt Youngs, but I’m giving massive props to Parrott for the first great pitching season in Mariners history.