When you think of Carl Yastrzemski, you think of 1967. When you think of Steve Carlton, you think of 1972.
You should—those were by far their best seasons.
In 1967, Yaz was worth 12.0 WAR as he captured the AL's Triple Crown. He hit .326/.418/.622 with 44 homers and 121 RBI in an offensively depressed era. He was even worth 23 runs in the field (which looks questionable until you see he had 22 the year before and 25 the year after. In 1967, Yaz was simply legit. His next-best season was 1968 with 10.0 WAR. Interestingly, that's the year he won the batting title with a .301 average. Now there's a lesson in era adjustments.
Steve Carlton's 1972 season was special because he won 27 games for a 59-win team. Beyond the wins, he led the league with a 1.97 ERA, 310 Ks and a 182 ERA+. He was worth 11.7 WAR (actually 12.1 if you add his offensive value). His next-best season was 1980, when he again led the league in wins, innings, and strikeouts while accumulating 9.9 WAR (9.8 with offense).
When you think of Roger Maris, what season pops into your mind? How about Babe Ruth? Lefty Grove? Ted Williams? Sometimes a player's iconic year does not match up with his most valuable one.
I'm sure most fans associate the name Roger Maris with the number 61—as in 61 home runs, 1961, and the film 61*. Maris had a historic 1961 season, surpassing Babe Ruth's single-season home run mark and driving in a ton of runs. For his effort, he earned 6.7 WAR and the MVP Award. His most valuable season, however, actually came the previous year in 1960—his first MVP season. While he hit 22 fewer home runs and drove in 29 fewer runs, his OPS+ was nearly on par with 1961 (160 in 1960, 167 in 1961). Because of a big difference in plate appearances, his WAR Batting Runs separate a but more (41 in 1960, 54 in 1961). In the field, however, Maris was worth 19 runs in 1960 and just a single run in 1961, giving him a 1960 WAR total of 7.3, or 0.6 more than his record-breaking season.
Fred Lynn is actually the player who inspired this research. Most associate Lynn with his Rookie of the Year/MVP campaign in 1975. Lynn led the league in doubles (47), slugging (.566), and runs scored (103) en route to 7.1 WAR. That's a magnificent number for a rookie and an appropriate one for an MVP. Four years later, in 1979, Lynn was actually worth 8.5 WAR. He led the league in every slash/rate stat (.333/.423/.637/1.059 OPS/176 OPS+), compiling 54 WAR batting runs (compared to 41 in 1975). He was nearly equal on defense in each season (8 runs in 1975, 9 runs in 1979), so the difference lies in the offense.
Many associate Joe DiMaggio and Ted Williams with their epic 1941 season. DiMaggio hit in 56 straight games and captured the MVP. Williams became the last player to hit .400. 1941 was indeed DiMaggio's best year (at 8.6 WAR). That total was dwarfed by Williams' 10.1 WAR, however. The crazy thing? That wasn't Williams' most valuable season.
Williams won two Triple Crowns, so it would make sense if these were his most valuable seasons. His 1942 season was, in fact, worth 10.2 WAR. He also won the Triple Crown in 1947 with a 9.5 WAR season. But Williams' most valuable season was not 1941 and not either of his Triple Crown seasons. Remarkably, it was the first season he returned from World War II—1946. Williams was worth 87 WAR batting runs (bested only by his 101 in 1941) but also scored well defensively, worth 4 runs. His traditional numbers included a .342/.497/.667 slash line, a 215 OPS+, 38 HR, and 123 RBI. He was worth 10.7 WAR.
And that was after three years off.
To fight in a goddamn war.
In my youth, I always associated Babe Ruth with 1927. After all, that was the year he hit 60 homer and was part of one of the most famous teams ever. While 1927 was Lou Gehrig's career year (11.5 WAR), it wasn't the Babe's.
Thanks to my many hours playing Earl Weaver Baseball, I learned that Ruth was even better in 1921. He hit 59 homers rather than 60, but had .378 batting average (vs. .356 in 1927), 171 RBI (vs. 164), and 457 total bases (vs. 417). WAR backs this up, rating Ruth at 12.6 WAR—a half win ahead of 1927's 12.1 WAR.
1921, however, still wasn't Ruth's most valuable season. It was actually 1923, the year he established career highs in batting average (.393), on base percentage (.545), hits (205), and doubles (45). His 114 WAR batting runs was two fewer than 1921, but he posted a career high 19 runs in the field. (Total Zone rates Ruth as an excellent fielder, worth 79 runs above average over his career.) The combination of offense and defense led to a career high 13.7 wins above replacement—Ruth's best year by a significant margin.
In 1931, Lefty Grove posted a breathtaking 31-4 record with league leading marks in ERA (2.06), strikeouts (175), and winning percentage (.886). He was worth 9.5 WAR as a pitcher. He value offensively was –0.4 WAR, making his net worth 9.1 WAR. He won the MVP award.
In 1936, Grove went "just" 17–12 with a league leading 2.81 ERA. Yet, he was worth 10.7 WAR on the hill. Similarly, Denny McLain was worth 6.8 WAR as a pitcher (and overall) in 1968, the year he was the Majors' last 30-game winner. The very next season, he won seven fewer games with an ERA 0.84 higher, but he was worth 7.5 WAR (7.2 WAR overall).
So, why weren't the iconic seasons worth as much? Both weren't for similar reasons. One small reason is that in the iconic season, both pitchers benefited from better defense behind them. The bigger reason, however, is run environments. Even the difference between 1968 and 1969 was a big one. 1968, of course, was the original Year of the Pitcher. That year, AL teams scored 3.41 runs per game. Just a year later, it was 4.09. That's a big difference. Grove's 1931 season is pretty remarkable because it happened when the run environment in the AL yielded 5.14 runs per game. But in 1936, it was even higher at 5.67.
The idea of iconic seasons not being as valuable as other seasons is not really a novel one. Most saberists know, for example, that Andre Dawson's MVP season in 1987 was far from his best campaign. It was worth 3.7 WAR. Dawson had seven other seasons of 3.7 WAR or better. Let's also take Bob Welch, the last pitcher to win 27 games. Welch was worth just 2.7 WAR that year (1990). He was also better than that in seven other seasons.
Finally, let's look at a couple relievers. I've been banging this drum for a while now, but most consider Dennis Eckersley to be a Hall of Fame reliever. He was much, much more valuable as a starter. His top WAR as a reliever was 3.2 in 1990. He had seven seasons as a starter where he was more valuable than that, including a 7.0 WAR season for the Red Sox in 1978.
And what was Mariano Rivera's most valuable season? Well, that'd of course be the one full season he pitched, but didn't close (1996). He was worth 4.8 WAR that year. His next highest was 4.2. That just shows how much innings pitched factors into WAR—Rivera threw 107.2 innings in 1996 (his career high by 27 IP).
Of course, I've used the new version of WAR published by Baseball-Reference for this research.