Harry Krause has the best ERA by a pitcher 20 or younger in a season, with an ERA of 1.39 in his rookie season in 1909.

Interpreted as:

lowest era with a minimum of 1 IP per team game by a player in a season age 20-

	NAME	ERA	AGE	SEASON	TM	G	W	L	W%	GS	SO	CG	SHO	SV	IP	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	Harry Krause H. Krause	1.39	20	1909	PHA	32	18	8	.692	21	139	16	7	0	213.0	151	33	49	2	49	13	8		801	2	5.87	2.07	2.84	0.08	17.4	6.1	0.94	.249	2.07	58	1.91	82	6.38	9.5
2	John Ward J. Ward	1.51	18	1878	PRO	37	22	13	.629	37	116	37	6	0	334.0	308	56	151	3	34		0		1,365	26	3.13	0.92	3.41	0.08	8.5	2.5	1.02		4.07	68	2.26	101	8.30	-4.4
3	Dwight Gooden D. Gooden	1.53	20	1985	NYM	35	24	4	.857	35	268	16	8	0	276.2	198	47	51	13	69	2	0	4	1,065	6	8.72	2.24	3.88	0.42	25.2	6.5	0.97	.259	1.66	44	2.12	59	6.44	45.6
4	Silver King S. King	1.63	20	1888	STL	66	45	20	.692	64	258	64	6	0	584.2	435	106	203	6	76	30	1		2,291	23	3.97	1.17	3.39	0.09	11.3	3.3	0.87	.223	3.12	50	2.38	76	6.70	55
5	Walter Johnson W. Johnson	1.65	20	1908	WSH	36	14	14	.500	30	160	23	6	1	256.1	194	47	75	0	53	11	6		985	13	5.62	1.86	3.02	0.00	16.2	5.4	0.96	.255	2.63	72	1.60	75	6.81	15
6	Frank Killen F. Killen	1.68	20	1891	MIL	11	7	4	.636	11	38	11	2	0	96.2	73	18	42	1	51	3	0		415	4	3.54	4.75	0.75	0.09	9.2	12.3	1.28	.224	3.91	41	3.55	90	6.80	6
7	Tommy Bond T. Bond	1.68	20	1876	HAR	45	31	13	.705	45	88	45	6	0	408.0	355	76	164	2	13		0		1,623	8	1.94	0.29	6.77	0.04	5.4	0.8	0.90		3.62	69	1.96	81	7.83	27.5
8	Joe Wood J. Wood	1.69	20	1910	BSA	35	12	13	.480	17	145	14	3	0	196.2	155	37	81	3	56	10	13		771	5	6.64	2.56	2.59	0.14	18.8	7.3	1.07	.273	3.71	67	2.05	78	7.09	12.4
9	John Ward J. Ward	1.74	20	1880	PRO	70	39	24	.619	67	230	59	8	1	595.0	501	115	230	5	45		4		2,351	19	3.48	0.68	5.11	0.08	9.8	1.9	0.92		3.48	76	2.10	91	7.58	9.3
10	Stump Wiedman S. Wiedman	1.80	20	1881	DET	13	8	5	.615	13	26	13	1	0	115.0	108	23	48	1	12		0		466	3	2.03	0.94	2.17	0.08	5.6	2.6	1.04		3.76	66	2.66	97	8.45	0.8
11	Larry Corcoran L. Corcoran	1.95	20	1880	CWS	63	43	14	.754	60	268	57	4	2	536.1	404	116	218	6	99		3		2,133	19	4.50	1.66	2.71	0.10	12.6	4.6	0.94		3.66	80	2.23	91	6.78	16.5
12	Pretzels Getzien P. Getzien	1.95	20	1884	DET	17	5	12	.294	17	107	17	1	0	147.1	118	32	73	2	25		0		604	9	6.54	1.53	4.28	0.12	17.7	4.1	0.97		4.46	66	2.51	75	7.21	13.7
13	Perry Werden P. Werden	1.97	18	1884	SLU	16	12	1	.923	16	51	12	1	0	141.1	113	31	61	1	22		0		575	5	3.25	1.40	2.32	0.06	8.9	3.8	0.96		3.88	67	3.11	121	7.20	-10
14	John Ward J. Ward	2.15	19	1879	PRO	70	47	19	.712	60	239	58	2	1	587.0	571	140	270	5	36		10		2,425	29	3.66	0.55	6.64	0.08	9.9	1.5	1.03		4.14	89	2.22	92	8.75	7.9
15	Joe Wood J. Wood	2.18	19	1909	BOS	24	11	7	.611	19	88	13	4	0	160.2	121	39	51	1	43	6	3		629	5	4.93	2.41	2.05	0.06	14.0	6.8	1.02	.244	2.86	88	2.12	87	6.78	5.6
16	Jose Fernandez J. Fernandez	2.19	20	2013	MIA	28	12	6	.667	28	187	0	0	0	172.2	111	42	47	10	58	5	0	5	681	3	9.75	3.02	3.22	0.52	27.5	8.5	0.98	.240	2.45	60	2.72	75	5.79	18.1
17	Ice Box Chamberlain I. Box Chamberlain	2.19	20	1888	TOT	38	25	11	.694	38	176	34	2	0	308.0	239	75	157	3	86	17	0		1,261	31	5.14	2.51	2.05	0.09	14.0	6.8	1.06	.241	4.59	69	2.57	84	6.98	18.2
18	Bill Vinton B. Vinton	2.23	19	1884	PHN	21	10	10	.500	21	105	20	0	0	182.0	166	45	131	6	35		0		789	20	5.19	1.73	3.00	0.30	13.3	4.4	1.10		6.48	76	3.13	94	8.21	3.1
19	Kid Nichols K. Nichols	2.23	20	1890	BSN	48	27	19	.587	47	222	47	7	0	424.0	374	105	175	8	112	11	1		1,755	30	4.71	2.38	1.98	0.17	12.6	6.4	1.15	.261	3.71	60	2.98	75	7.94	51
20	Scott Stratton S. Stratton	2.36	20	1890	LOU	50	34	14	.708	49	207	44	4	0	431.0	398	113	186	3	61	13	1		1,749	7	4.32	1.27	3.39	0.06	11.8	3.5	1.06	.270	3.88	64	2.56	73	8.31	41.7
21	Will Sawyer W. Sawyer	2.36	18	1883	CLE	17	4	10	.286	15	76	15	0	0	141.0	119	37	79	1	47		2		596	13	4.85	3.00	1.62	0.06	12.8	7.9	1.18		5.04	77	3.27	106	7.60	-3.9
22	Johnny Lush J. Lush	2.37	20	1906	PHN	37	18	15	.545	35	151	24	5	0	281.0	254	74	128	2	119	16	1		1,210	8	4.84	3.81	1.27	0.06	12.5	9.8	1.33	.273	4.10	91	2.83	104	8.14	-4.1
23	Christy Mathewson C. Mathewson	2.41	20	1901	NYG	40	20	17	.541	38	221	36	5	0	336.0	288	90	131	3	97	13	2		1,361	23	5.92	2.60	2.28	0.08	16.2	7.1	1.15	.278	3.51	73	2.71	83	7.71	20.8
24	Babe Ruth B. Ruth	2.44	20	1915	BSA	32	18	8	.692	28	112	16	1	0	217.2	166	59	80	3	85	6	3		874	9	4.63	3.51	1.32	0.12	12.8	9.7	1.15	.244	3.31	85	2.81	97	6.86	1.8
25	Dick Burns D. Burns	2.46	20	1884	CNU	40	23	15	.605	40	167	34	1	0	329.2	298	90	179	7	47		0		1,371	17	4.56	1.28	3.55	0.19	12.2	3.4	1.05		4.89	77	2.96	107	8.14	-2.1