Which teams' actual ERAs were the farthest below their FIP ERAs since 1900?

Data used here comes from Fangraphs and Baseball Reference. In the table below, DER is defensive efficiency rating. That is the percentage of balls in play converted into outs. Rank is where the team ranked in DER in their league for that year. Lg Avg is the league average DER for that year.

Team	Year	ERA	FIP	Diff	DER	Rank	Lg Avg
Yankees	1939	3.31	4.26	-0.95	0.694	1	0.685
Giants	1933	2.71	3.49	-0.78	0.719	1	0.702
Giants	1934	3.19	3.95	-0.76	0.704	1	0.685
Reds	1999	3.99	4.74	-0.75	0.722	1	0.687
Giants	1954	3.09	3.83	-0.74	0.722	1	0.707
Athletics	1929	3.44	4.16	-0.72	0.703	1	0.687
Giants	1936	3.46	4.18	-0.72	0.693	2	0.684
Indians	1948	3.22	3.94	-0.72	0.731	1	0.704
Braves	2002	3.13	3.83	-0.70	0.712	2	0.695
Twins	1965	3.14	3.84	-0.70	0.724	3	0.715
Robins	1930	4.03	4.72	-0.69	0.693	1	0.669
Cubs	1906	1.75	2.43	-0.68	0.736	1	0.698
Cubs	1935	3.26	3.93	-0.67	0.696	2	0.686
Reds	1939	3.27	3.94	-0.67	0.708	1	0.695
Yankees	1955	3.23	3.89	-0.66	0.733	1	0.710
Orioles	1973	3.08	3.74	-0.66	0.731	1	0.701
Yankees	1935	3.60	4.26	-0.66	0.713	1	0.687
Bees	1937	3.22	3.88	-0.66	0.714	1	0.689
Athletics	1990	3.18	3.84	-0.66	0.732	1	0.699
Braves	1956	3.10	3.75	-0.65	0.726	2	0.716
White Sox	1967	2.45	3.10	-0.65	0.735	1	0.718
Reds	1940	3.05	3.69	-0.64	0.730	1	0.701
Giants	1931	3.30	3.93	-0.63	0.706	1	0.687
Yankees	1957	3.00	3.62	-0.62	0.727	1	0.713
Tigers	1982	3.81	4.43	-0.62	0.725	1	0.704

Twenty of the top 25 teams ranked first in DER. That makes sense, since if you turn alot of balls in play into outs, you will give up fewer runs (and fewer than expected based on walks, strikeouts and HRs, which figure into FIP ERA). The 1939 Yankees had a 106-45 record and the all-time best run differential of 411.

Teams might also see their actual ERA go below their FIP ERA if they pitch well with runners on base. But my post last week showed that although that matters, DER probably matters more.

Twelve of these 25 teams came between 1929 & 1940 (I wonder what the reason is). Many of the 25 were pennant winners or made the playoffs.

Four Giants teams from the 1930s are on the list. They led the NL in DER 4 times in the decade and were 2nd three times. They also led in fielding pct. 4 times with one 2nd. They had the highest DER for the decade of 0.7001 (2nd place had 0.6960). Maybe they are one of the great fielding teams in baseball history. But it is not anything I have ever heard about.