fewest unearned runs allowed in 1 season by team 1903 to 2019

Between the 1903 and 2019 seasons, the Houston Astros allowed the fewest runs by a team in a season, with 331 runs in 1981.

	TEAM	R	SEASON	G	W%	W	L	GS	ERA	SO	CG	SHO	SV	IP	H	ER	HR	BB	HBP	IBB	TBF	WP	K/9	BB/9	K/BB	HR/9	K%	BB%	WHIP	BABIP	RA	H/9
1	Astros	331	1981	110	.555	61	49	110	2.66	610	23	13	25	990.0	842	293	40	300	11	24	4,034	36	5.55	2.73	2.03	0.36	15.1	7.4	1.15	.261	3.01	7.65
2	Yankees	343	1981	107	.551	59	48	107	2.90	606	16	0	30	948.0	827	305	64	287	10	17	3,872	25	5.75	2.72	2.11	0.61	15.7	7.4	1.18	.263	3.26	7.85
3	Dodgers	356	1981	110	.573	63	47	110	3.01	603	26	15	24	997.0	904	333	54	302	14	38	4,099	19	5.44	2.73	2.00	0.49	14.7	7.4	1.21	.272	3.21	8.16
4	Red Sox	381	1918	126	.595	75	51	126	2.31	392	105	25	2	1120.0	931	287	9	380	31		4,557	29	3.15	3.05	1.03	0.07	8.6	8.3	1.17	.246	3.06	7.48
5	Cubs	381	1906	155	.763	116	36	155	1.75	702	125	28	10	1388.1	1,018	270	12	446	53		5,427	20	4.55	2.89	1.57	0.08	12.9	8.2	1.05	.239	2.47	6.60
6	Rangers	389	1981	105	.543	57	48	105	3.40	488	23	10	18	940.1	851	355	67	322	17	34	3,909	18	4.67	3.08	1.52	0.64	12.5	8.2	1.25	.260	3.72	8.14
7	Cubs	389	1909	155	.680	104	49	155	1.74	680	111	32	11	1409.1	1,094	272	6	364	38		5,494	30	4.34	2.32	1.87	0.04	12.4	6.6	1.03	.247	2.48	6.99
8	Cubs	390	1907	155	.704	107	45	155	1.73	586	114	31	8	1373.1	1,054	264	11	402	38		5,315	25	3.84	2.63	1.46	0.07	11.0	7.6	1.06	.244	2.56	6.91
9	Cubs	393	1918	131	.651	84	45	131	2.18	472	92	21	8	1197.0	1,050	290	13	296	22		4,843	19	3.55	2.23	1.59	0.10	9.7	6.1	1.12	.257	2.95	7.89
10	Expos	394	1981	108	.556	60	48	108	3.30	520	20	8	23	975.0	902	357	58	268	18	21	4,008	28	4.80	2.47	1.94	0.54	13.0	6.7	1.20	.268	3.64	8.33
11	Reds	401	1919	140	.686	96	44	140	2.23	407	89	23	9	1274.0	1,104	316	21	298	20		5,063	12	2.88	2.11	1.37	0.15	8.0	5.9	1.10	.251	2.83	7.80
12	Athletics	403	1981	109	.587	64	45	109	3.30	505	60	11	10	993.0	883	364	80	370	28	17	4,166	30	4.58	3.35	1.36	0.73	12.1	8.9	1.26	.252	3.65	8.00
13	Tigers	404	1981	109	.550	60	49	109	3.53	476	33	6	22	969.1	840	380	83	373	27	41	4,030	24	4.42	3.46	1.28	0.77	11.8	9.3	1.25	.246	3.75	7.80
14	Royals	405	1981	103	.485	50	53	103	3.56	404	24	4	24	922.1	909	365	75	273	20	36	3,878	13	3.94	2.66	1.48	0.73	10.4	7.0	1.28	.269	3.95	8.87
15	Cubs	407	1919	140	.536	75	65	140	2.21	495	80	21	5	1265.0	1,127	311	14	294	28		5,109	20	3.52	2.09	1.68	0.10	9.7	5.8	1.12	.260	2.90	8.02
16	Senators	408	1918	130	.563	72	56	130	2.14	505	75	19	8	1228.0	1,021	292	10	395	28		4,954	35	3.70	2.89	1.28	0.07	10.2	8.0	1.15	.252	2.99	7.48
17	Pirates	412	1918	126	.520	65	60	126	2.48	367	85	8	7	1140.1	1,005	314	13	299	32		4,608	12	2.90	2.36	1.23	0.10	8.0	6.5	1.14	.255	3.25	7.93
18	Giants	414	1981	111	.505	56	55	111	3.28	561	8	3	33	1009.1	970	368	57	393	24	56	4,302	36	5.00	3.50	1.43	0.51	13.0	9.1	1.35	.279	3.69	8.65
19	Giants	415	1918	124	.573	71	53	124	2.64	330	74	17	11	1111.2	1,002	326	20	228	23		4,493	20	2.67	1.85	1.45	0.16	7.3	5.1	1.11	.252	3.36	8.11
20	Braves	416	1981	107	.472	50	56	107	3.45	471	11	4	24	968.0	936	371	62	330	11	31	4,078	25	4.38	3.07	1.43	0.58	11.5	8.1	1.31	.273	3.87	8.70
21	Athletics	416	1909	153	.621	95	58	153	1.93	728	110	27	3	1378.0	1,069	296	9	386	65		5,385	31	4.75	2.52	1.89	0.06	13.5	7.2	1.06	.253	2.72	6.98
22	Cardinals	417	1981	103	.578	59	43	103	3.63	388	11	2	33	943.0	902	380	52	290	15	45	3,910	22	3.70	2.77	1.34	0.50	9.9	7.4	1.26	.269	3.98	8.61
23	White Sox	423	1981	106	.509	54	52	106	3.47	529	20	6	23	940.2	891	363	73	336	24	17	3,964	24	5.06	3.21	1.57	0.70	13.3	8.5	1.30	.272	4.05	8.52
24	Pirates	425	1981	103	.451	46	56	103	3.56	492	11	4	29	942.0	953	373	60	346	15	51	4,029	32	4.70	3.31	1.42	0.57	12.2	8.6	1.38	.287	4.06	9.11
25	Orioles	430	1972	154	.519	80	74	154	2.53	788	62	18	21	1371.2	1,116	386	85	395	15	52	5,493	35	5.17	2.59	1.99	0.56	14.3	7.2	1.10	.245	2.82	7.32