One of the first major impacts Bill James made as a sabermetrician was pointing out the huge effect that ballparks had on statistics. I mean, people always knew that Fenway Park and Wrigley Field were good hitting parks, or that the Astrodome was a lousy place to hit home runs, but that doesn't mean people in the game properly accounted for these factors. For decades, the Cubs always overrated their hitters and underrated their pitchers. That was one reason they were the Cubs.
Obvoiusly, a park can drastically effect our view of a player if we're not aware of the advantage he's receiving from his home park. Here are a few historical players who received a big boost from their home park or parks.
When Jim Rice hit the Hall of Fame ballot after his 16-year career with the Red Sox, the debates got ugly. Rice was feared, argued his supporters; Rice was overrated, a beneficiary of Fenway Park, argued his detractors. During most of Rice's career in Boston, Fenway was a terrific hitter's park, the traditional Fenway of "no lead is safe" lore. Overall, Rice hit .320 with 208 home runs at Fenway but .277 with 174 home runs on the road. In his 1978 MVP season, Rice hit .361/.416/.690 with 28 home runs at home and .269/.325/.512 with 18 home runs on the road. The debates lasted until Rice's 15th and final year on the ballot when he made it in.
Through 1961, Koufax was 54-53 in his career with a 3.94 ERA, a talented but erratic left-hander. Suddenly, in 1962, he put it all together, and over his final five seasons in the majors went 111-34 with a 1.95 ERA, leading the NL in ERA all five seasons. Koufax's control did improve dramatically, but something else happened in 1962: The Dodgers moved out of the L.A. Coliseum and into Dodger Stadium. In 1961, Koufax had a 2.77 ERA on the road but 4.22 at home. In 1960, he had 3.00 ERA on the road but 5.27 at home. In 1962, Koufax had a 3.53 ERA on the road but 1.75 at home. In 1963, he was 2.31 on the road and 1.38 at home. He had always been pretty good on the road, but the difference was he became unhittable at Dodger Stadium.
Before finishing his legendary career with the Rangers, Ryan spent eight seasons with the Angels and nine with the Astros; that's 17 years in parks that heavily favored pitchers. Check out his career home/road splits, including his days with the Mets and Rangers: 189-136, 2.77 ERA at home; 135-156, 3.73 ERA on the road. Yes, Ryan had a career road record 21 games under .500.
Sandberg made the Hall of Fame in his third year on the ballot, with his reputation as an all-around player -- power, speed, defense -- overcoming some career counting stats that might be considered marginal for a Hall of Famer: 2,386 hits, 282 home runs, 1,061 RBI and a .285 average. But those totals would look even more marginal without a little help from Wrigley Field. Sandberg hit .300/.361/.491 with 164 home runs at home and .269/.326/.412 with 118 home runs on the road. (Ernie Banks, by the way, had a similar split: .290 at Wrigley and .259 on the road.)
Ott hit 511 career home runs and led the NL in homers six times but took advantage of the short porch at the Polo Grounds to do so. He hit 323 home runs at home and 188 on the road. He was still a great hitter, however; on the road, he hit more doubles and triples and hit for a higher average, so his overall batting line was still an impressive .311/.408/.510 compared to .297/.422/.558 at home. But he wouldn't be a member of the 500-home run club if he'd played elsewhere.
Fenway Park isn't the hitter's park it used to be. It's believed that renovations in 1988, which moved a new press box above the stadium club seats behind home plate, changed the air currents. It's also underrated as a good park for left-handed hitters, especially those who can go the opposite way and take advantage of the Green Monster. Yaz hit 237 home runs at home and 215 on the road, but he loved hitting at Fenway, with a .306 average there compared to .264 on the road. His OPS was 125 points higher at home than on the road. (Ted Williams hit .361 at Fenway and .328 on the road.)
Like Koufax, Sutton enjoyed pitching at Dodger Stadium. He went 169-119, 2.81 at home in his career and 155-137, 3.77 on the road. Thirty-nine of his 58 shutouts came at home. Pulling out Dodger Stadium individually (which includes some road games when he pitched for the Astros), Sutton posted a 2.66 ERA there. Despite winning 300 games, he was a somewhat controversial Hall of Fame selection; he might have still won 300 games for another organization, but his ERA might have been a bit higher.
Would any of these guys not be a Hall of Famer without their home parks? It's difficult to say. Extreme talents can learn to take advantage of unique situations. But maybe Koufax's curveball was better because of the high mound at Dodger Stadium, or Ryan's fastball harder to pick up in the gloomy indoor lighting of the Astrodome. Rice, in particular, had a weak Hall of Fame case as-is; if he hadn't played for the Red Sox, I doubt he'd be in Cooperstown.