Since 1900, the Kansas City Royals have the worst ERA by a team in a month, with an ERA of 18.00 in October 1995.

	TEAM	ERA	MONTH	G	W%	W	L	SO	SHO	SV	IP	H	ER	R	HR	BB	HBP	IBB	TBF	WP	K/9	BB/9	K/BB	HR/9	K%	BB%	WHIP	BABIP	RA	H/9
1	Royals	18.00	October 1995	1	.000	0	1	7	0	0	8.0	19	16	17	2	5	0	0	48	0	7.88	5.63	1.40	2.25	14.6	10.4	3.00	.500	19.13	21.38
2	Orioles	16.20	October 2006	1	.000	0	1	4	0	0	5.0	7	9	9	3	5	1	0	27	0	7.20	9.00	0.80	5.40	14.8	18.5	2.40	.286	16.20	12.60
3	Mets	15.00	March 2003	1	.000	0	1	6	0	0	9.0	16	15	15	2	12	0	0	53	0	6.00	12.00	0.50	2.00	11.3	22.6	3.11	.424	15.00	16.00
4	Rangers	14.00	March 2014	1	.000	0	1	8	0	0	9.0	17	14	14	3	6	0	0	50	1	8.00	6.00	1.33	3.00	16.0	12.0	2.56	.424	14.00	17.00
5	Twins	13.50	October 2000	1	.000	0	1	5	0	0	8.0	19	12	12	1	5	0	0	46	0	5.63	5.63	1.00	1.13	10.9	10.9	3.00	.514	13.50	21.38
6	Cubs	12.38	March 1998	1	.000	0	1	9	0	0	8.0	14	11	11	2	4	1	0	43	1	10.13	4.50	2.25	2.25	20.9	9.3	2.25	.444	12.38	15.75
7	Brewers	12.27	March 2025	4	.000	0	4	28	0	0	33.0	48	45	47	17	21	5	1	172	1	7.64	5.73	1.33	4.64	16.3	12.2	2.09	.307	12.82	13.09
8	Blue Jays	12.00	October 2023	1	.000	0	1	9	0	0	9.0	16	12	12	3	3	1	0	47	2	9.00	3.00	3.00	3.00	19.1	6.4	2.11	.419	12.00	16.00
9	Royals	12.00	October 2017	1	.000	0	1	8	0	0	9.0	16	12	14	2	8	0	0	52	0	8.00	8.00	1.00	2.00	15.4	15.4	2.67	.412	14.00	16.00
10	Phillies	11.25	March 2023	1	.000	0	1	8	0	0	8.0	10	10	11	2	6	0	0	38	0	9.00	6.75	1.33	2.25	21.1	15.8	2.00	.364	12.38	11.25
11	Mets	11.25	October 2017	1	.000	0	1	11	0	0	8.0	11	10	11	2	7	0	0	42	0	12.38	7.88	1.57	2.25	26.2	16.7	2.25	.409	12.38	12.38
12	Rockies	11.25	March 2014	1	.000	0	1	11	0	0	8.0	14	10	10	1	2	1	0	41	0	12.38	2.25	5.50	1.13	26.8	4.9	2.00	.500	11.25	15.75
13	White Sox	11.25	March 2008	1	.000	0	1	9	0	0	8.0	12	10	10	2	3	0	1	38	0	10.13	3.38	3.00	2.25	23.7	7.9	1.88	.417	11.25	13.50
14	Giants	11.25	October 1995	1	.000	0	1	1	0	0	8.0	15	10	10	2	4	1	3	42	0	1.13	4.50	0.25	2.25	2.4	9.5	2.38	.382	11.25	16.88
15	Astros	11.25	October 1967	1	.000	0	1	8	0	0	8.0	16	10	10	2	3	0	1	44	0	9.00	3.38	2.67	2.25	18.2	6.8	2.38	.452	11.25	18.00
16	Nationals	11.00	October 2017	1	.000	0	1	10	0	0	9.0	14	11	11	0	7	2	0	48	0	10.00	7.00	1.43	0.00	20.8	14.6	2.33	.483	11.00	14.00
17	Devil Rays	11.00	March 1998	1	.000	0	1	7	0	0	9.0	18	11	11	1	2	0	0	47	0	7.00	2.00	3.50	1.00	14.9	4.3	2.22	.459	11.00	18.00
18	Royals	10.50	October 2009	3	.000	0	3	14	0	0	24.0	31	28	28	8	14	1	0	116	0	5.25	5.25	1.00	3.00	12.1	12.1	1.88	.291	10.50	11.63
19	Orioles	10.13	October 2021	3	.000	0	3	13	0	0	24.0	38	27	28	11	6	2	0	117	2	4.88	2.25	2.17	4.13	11.1	5.1	1.83	.318	10.50	14.25
20	Blue Jays	10.13	March 2014	1	.000	0	1	6	0	0	8.0	11	9	9	0	8	2	0	44	1	6.75	9.00	0.75	0.00	13.6	18.2	2.38	.393	10.13	12.38
21	Blue Jays	10.13	October 2000	1	.000	0	1	7	0	0	8.0	12	9	11	4	1	1	0	38	0	7.88	1.13	7.00	4.50	18.4	2.6	1.63	.320	12.38	13.50
22	Royals	10.13	October 1990	2	.000	0	2	11	0	0	16.0	22	18	18	0	12	0	0	80	5	6.19	6.75	0.92	0.00	13.8	15.0	2.13	.386	10.13	12.38
23	Cubs	10.13	October 1967	1	.000	0	1	5	0	0	8.0	12	9	10	2	3	0	0	35	0	5.63	3.38	1.67	2.25	14.3	8.6	1.88	.400	11.25	13.50
24	Braves	10.00	October 2023	1	.000	0	1	1	0	0	9.0	15	10	10	0	6	0	1	47	0	1.00	6.00	0.17	0.00	2.1	12.8	2.33	.375	10.00	15.00
25	Cardinals	10.00	March 2023	1	.000	0	1	11	0	0	9.0	19	10	10	0	3	1	0	49	1	11.00	3.00	3.67	0.00	22.4	6.1	2.44	.559	10.00	19.00