least era in a season while pitching at least 30 ip

Buck O'Brien has the lowest ERA with 30.0+ innings pitched in a season, with an ERA of 0.38 in his rookie season in 1911.

Interpreted as:

least era by a player in a season while pitching at least 30 ip

	NAME	ERA	IP	SEASON	TM	G	W	L	W%	GS	SO	CG	SHO	SV	H	ER	R	HR	BB	HBP	GF	IBB	TBF	WP	K/9	BB/9	K/BB	HR/9	K%	BB%	WHIP	BABIP	RA	ERA-	FIP	FIP-	H/9	PRAA
1	Buck O'Brien B. O'Brien	0.38	47.2	1911	BSA	6	5	1	.833	5	31	5	2	0	30	2	9	0	21	1	1		189	0	5.85	3.97	1.48	0.00	16.4	11.1	1.07	.221	1.70	11	2.85	88	5.66	2
2	Kevin Siegrist K. Siegrist	0.45	39.2	2013	STL	45	3	1	.750	0	50	0	0	0	17	2	2	1	18	1	15	1	152	0	11.34	4.08	2.78	0.23	32.9	11.8	0.88	.195	0.45	12	2.29	61	3.86	6.4
3	Zack Britton Z. Britton	0.54	67.0	2016	BAL	69	2	1	.667	0	74	0	0	47	38	4	7	1	18	0	63	3	254	10	9.94	2.42	4.11	0.13	29.1	7.1	0.84	.230	0.94	13	1.93	44	5.10	17.7
4	Joey Devine J. Devine	0.59	45.2	2008	OAK	42	6	1	.857	0	49	0	0	1	23	3	7	0	15	0	10	2	170	0	9.66	2.96	3.27	0.00	28.8	8.8	0.83	.217	1.38	14	1.96	46	4.53	11.7
5	Fernando Rodney F. Rodney	0.60	74.2	2012	TBR	76	2	2	.500	0	76	0	0	48	43	5	9	2	15	3	65	1	282	4	9.16	1.81	5.07	0.24	27.0	5.3	0.78	.220	1.08	16	2.12	52	5.18	16.2
6	Emmanuel Clase E. Clase	0.61	74.1	2024	CLE	74	4	2	.667	0	66	0	0	47	39	5	10	2	10	2	66	1	270	2	7.99	1.21	6.60	0.24	24.4	3.7	0.66	.195	1.21	15	2.22	55	4.72	15.2
7	Dennis Eckersley D. Eckersley	0.61	73.1	1990	OAK	63	4	2	.667	0	73	0	0	48	41	5	9	2	4	0	61	1	262	0	8.96	0.49	18.25	0.25	27.9	1.5	0.61	.213	1.10	17	1.33	35	5.03	20.6
8	George McQuillan G. McQuillan	0.66	41.0	1907	PHN	6	4	0	1.000	5	28	5	3	0	21	3	3	0	11	1	1		145	1	6.15	2.41	2.55	0.00	19.3	7.6	0.78	.200	0.66	27	1.69	64	4.61	4.3
9	Casey Sadler C. Sadler	0.67	40.1	2021	SEA	42	0	1	.000	0	37	0	0	0	19	3	4	1	10	1	2	0	145	2	8.26	2.23	3.70	0.22	25.5	6.9	0.72	.188	0.89	16	2.47	59	4.24	7.7
10	Hank Aguirre H. Aguirre	0.69	39.0	1968	LAD	25	1	2	.333	0	25	0	0	3	32	3	8	0	13	3	16	3	167	4	5.77	3.00	1.92	0.00	15.0	7.8	1.15	.254	1.85	25	2.33	90	7.38	1.1
11	Ray Searage R. Searage	0.70	38.1	1984	MIL	21	2	1	.667	0	29	0	0	6	20	3	3	0	16	1	16	3	149	1	6.81	3.76	1.81	0.00	19.5	10.7	0.94	.194	0.70	18	2.58	66	4.70	5.8
12	Rob Murphy R. Murphy	0.72	50.1	1986	CIN	34	6	0	1.000	0	36	0	0	1	26	4	4	0	21	0	12	2	195	5	6.44	3.75	1.71	0.00	18.5	10.8	0.93	.188	0.72	19	2.58	67	4.65	7
13	Mike Adams M. Adams	0.73	37.0	2009	SDP	37	0	0		0	45	0	0	0	14	3	9	1	8	0	5	1	136	1	10.95	1.95	5.63	0.24	33.1	5.9	0.59	.159	2.19	19	1.65	41	3.41	10.2
14	Jesse Crain J. Crain	0.74	36.2	2013	CWS	38	2	3	.400	0	46	0	0	0	31	3	6	0	11	1	5	1	152	0	11.29	2.70	4.18	0.00	30.3	7.2	1.15	.330	1.47	18	1.52	37	7.61	10.2
15	Laurie Reis L. Reis	0.75	36.0	1877	CWS	4	3	1	.750	4	11	4	1	0	29	3	8	1	6		0		142	3	2.75	1.50	1.83	0.25	7.7	4.2	0.97		2.00	26	3.09	106	7.25	-0.2
16	Barry Latman B. Latman	0.76	47.2	1958	CWS	13	3	0	1.000	3	28	1	1	0	27	4	7	1	17	1	3	0	188	1	5.29	3.21	1.65	0.19	14.9	9.0	0.92	.184	1.32	20	2.71	73	5.10	5.5
17	Rich Gossage R. Gossage	0.77	46.2	1981	NYY	32	3	2	.600	0	48	0	0	20	22	4	6	2	14	1	30	1	173	1	9.26	2.70	3.43	0.39	27.7	8.1	0.77	.185	1.16	22	2.06	57	4.24	8.3
18	Blake Treinen B. Treinen	0.78	80.1	2018	OAK	68	9	2	.818	0	100	0	0	38	46	7	12	2	21	1	58	3	315	6	11.20	2.35	4.76	0.22	31.7	6.7	0.83	.230	1.34	19	1.81	44	5.15	21
19	Earl Hamilton E. Hamilton	0.83	54.0	1918	PIT	6	6	0	1.000	6	20	6	1	0	47	5	7	0	13	0	0		210	1	3.33	2.17	1.54	0.00	9.5	6.2	1.11	.266	1.17	30	2.21	80	7.83	3.3
20	Nick Maddox N. Maddox	0.83	54.0	1907	PIT	6	5	1	.833	6	38	6	1	0	32	5	8	0	13	4	0		197	1	6.33	2.17	2.92	0.00	19.3	6.6	0.83	.225	1.33	34	1.72	65	5.33	5.5
21	Randy Rodríguez R. Rodríguez	0.84	32.0	2025	SFG	31	3	1	.750	0	46	0	0	1	18	3	5	1	5	1	7	0	118	1	12.94	1.41	9.20	0.28	39.0	4.2	0.72	.262	1.41	21	1.15	30	5.06	9.9
22	Tim Keefe T. Keefe	0.86	105.0	1880	TRO	12	6	6	.500	12	39	12	0	0	68	10	27	0	16		0		397	1	3.34	1.37	2.44	0.00	9.8	4.0	0.80		2.31	35	2.25	91	5.83	3.6
23	Cisco Carlos C. Carlos	0.86	41.2	1967	CWS	8	2	0	1.000	7	27	1	1	0	23	4	5	0	9	1	1	0	158	1	5.83	1.94	3.00	0.00	17.1	5.7	0.77	.190	1.08	28	1.96	60	4.97	6.1
24	Bill Henry B. Henry	0.87	52.0	1964	CIN	37	2	2	.500	0	28	0	0	6	31	5	9	2	12	3	20	4	202	1	4.85	2.08	2.33	0.35	13.9	5.9	0.83	.185	1.56	24	2.89	82	5.37	3.6
25	Bill Harris B. Harris	0.87	31.0	1931	PIT	4	2	2	.500	4	10	3	1	0	21	3	6	0	9	0	0		121	0	2.90	2.61	1.11	0.00	8.3	7.4	0.97	.206	1.74	23	3.34	84	6.10	2.2