Walter Johnson and Irv Young are tied for losing the most games in a month, with 9 games.

	NAME	L	MONTH	W	L%	G	W%	GS	ERA	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	H/9
1	Walter Johnson W. Johnson	9	July 1909	1	.900	10	.100	10		48	7	0	0	71.1	69		38	0	15	2	0		298	3	6.06	1.89	3.20	0.00	16.1	5.0	1.18	.296	4.79	8.71
2	Irv Young I. Young	9	July 1907	0	1.000	10	.000	8		17	6	0	1	60.1	78		43	1	15	3	2		265	1	2.54	2.24	1.13	0.15	6.4	5.7	1.54	.336	6.41	11.64
3	Wilbur Wood W. Wood	8	June 1973	1	.889	9	.111	9	4.43	42	5	0	0	69.0	78	34	38	10	23	1	0	2	300	1	5.48	3.00	1.83	1.30	14.0	7.7	1.46	.304	4.96	10.17
4	Scott Perry S. Perry	8	June 1918	1	.889	9	.111	8	3.65	22	8	0	0	69.0	81	28	30	1	22	0	0		288	2	2.87	2.87	1.00	0.13	7.6	7.6	1.49	.329	3.91	10.57
5	Buster Brown B. Brown	8	July 1910	1	.889	10	.111	7		25	5	1	1	63.2	52		28	2	18	1	2		244	4	3.53	2.54	1.39	0.28	10.2	7.4	1.10	.253	3.96	7.35
6	Bill Hogg B. Hogg	8	August 1908	0	1.000	8	.000	8		25	3	0	0	51.1	46		28	2	27	0	0		223	1	4.38	4.73	0.93	0.35	11.2	12.1	1.42	.260	4.91	8.06
7	Gus Dorner G. Dorner	8	August 1906	1	.889	9	.111	8		24	8	0	0	67.2	80		49	1	27	6	1		302	1	3.19	3.59	0.89	0.13	7.9	8.9	1.58	.324	6.52	10.64
8	Archie Stimmel A. Stimmel	8	September 1901	1	.889	9	.111	9	4.48	25	7	0	0	68.1	83	34	48	7	24	4	0			2	3.29	3.16	1.04	0.92		9.5	1.57	.396	6.32	10.93
9	Harry Howell H. Howell	8	August 1901	2	.800	10	.200	10	4.27	15	9	1	0	80.0	98		54	1	19	4	0			1	1.69	2.14	0.79	0.11		5.4	1.46	.312	6.08	11.03
10	Keith Atherton K. Atherton	7	August 1986	0	1.000	13	.000	0	5.59	13	0	0	0	19.1	23	12	15	5	11	1	8	2	92	1	6.05	5.12	1.18	2.33	14.1	12.0	1.76	.290	6.98	10.71
11	Jesse Jefferson J. Jefferson	7	August 1980	0	1.000	8	.000	6	8.10	15	0	0	0	33.1	39	30	32	2	18	2	1	1	153	0	4.05	4.86	0.83	0.54	9.8	11.8	1.71	.319	8.64	10.53
12	Jerry Koosman J. Koosman	7	August 1977	0	1.000	7	.000	7	4.60	32	2	0	0	47.0	53	24	28	5	18	1	0	5	204	0	6.13	3.45	1.78	0.96	15.7	8.8	1.51	.324	5.36	10.15
13	Dave Freisleben D. Freisleben	7	July 1976	0	1.000	8	.000	7	6.37	14	0	0	1	35.1	42	25	27	3	20	2	1	1	163	1	3.57	5.09	0.70	0.76	8.6	12.3	1.75	.315	6.88	10.70
14	Dick Ellsworth D. Ellsworth	7	July 1966	1	.875	8	.125	8	8.25	25	1	0	0	48.0	73	44	49	10	12	2	0	3	230	1	4.69	2.25	2.08	1.88	10.9	5.2	1.77	.348	9.19	13.69
15	Roger Craig R. Craig	7	July 1963	0	1.000	9	.000	7	4.47	10	5	0	0	46.1	42	23	30	6	11	0	2	0	191	2	1.94	2.14	0.91	1.17	5.2	5.8	1.14	.220	5.83	8.16
16	Roger Craig R. Craig	7	July 1962	1	.875	8	.125	7	4.15	28	3	0	0	52.0	52	24	27	9	13	2	1	0	212	1	4.85	2.25	2.15	1.56	13.2	6.1	1.25	.269	4.67	9.00
17	Johnny Schmitz J. Schmitz	7	June 1947	0	1.000	8	.000	5	5.40	23	0	0	1	33.1	42	20	26	3	10	0	3		156	2	6.21	2.70	2.30	0.81	14.7	6.4	1.56	.325	7.02	11.34
18	Early Wynn E. Wynn	7	July 1944	0	1.000	9	.000	6	6.28	15	3	0	0	43.0	63	30	36	1	17	1	2		205	1	3.14	3.56	0.88	0.21	7.3	8.3	1.86	.363	7.53	13.19
19	Hugh Mulcahy H. Mulcahy	7	August 1940	0	1.000	7	.000	7	4.88	11	2	0	0	48.0	54	26	33	3	13	0	0		209	1	2.06	2.44	0.85	0.56	5.3	6.2	1.40	.280	6.19	10.13
20	Max Butcher M. Butcher	7	September 1938	0	1.000	7	.000	7	3.81	17	6	0	0	54.1	52	23	28	4	19	2	0		235	0	2.82	3.15	0.89	0.66	7.2	8.1	1.31	.249	4.64	8.61
21	Joe Bowman J. Bowman	7	August 1936	0	1.000	9	.000	6	6.41	13	3	0	0	46.1	64	33	37	2	10	1	1		212	1	2.53	1.94	1.30	0.39	6.1	4.7	1.60	.333	7.19	12.43
22	Claude Passeau C. Passeau	7	August 1936	2	.778	10	.222	8	3.45	15	3	1	0	60.0	65	23	34	0	16	2	1		257	0	2.25	2.40	0.94	0.00	5.8	6.2	1.35	.290	5.10	9.75
23	Paul Derringer P. Derringer	7	July 1933	1	.875	9	.125	8	2.11	24	4	0	1	55.1	53	13	22	1	10	2	1		224	1	3.90	1.63	2.40	0.16	10.7	4.5	1.14	.278	3.58	8.62
24	Ray Benge R. Benge	7	July 1933	0	1.000	8	.000	8	4.07	18	2	0	0	55.1	64	25	30	3	8	1	0		235	0	2.93	1.30	2.25	0.49	7.7	3.4	1.30	.298	4.88	10.41
25	George Blaeholder G. Blaeholder	7	June 1933	3	.700	10	.300	9	5.82	18	3	0	0	60.1	77	39	47	9	16	0	1		264	1	2.69	2.39	1.13	1.34	6.8	6.1	1.54	.308	7.01	11.49