Jack Katoll has given up the most runs in a month, with 74 runs in September 1902.

Interpreted as:

most runs allowed by a player in a month

	NAME	R	MONTH	G	W	L	W%	GS	ERA	SO	CG	SHO	SV	IP	H	ER	HR	BB	HBP	GF	TBF	WP	K/9	BB/9	K/BB	HR/9	K%	BB%	WHIP	BABIP	RA	H/9
1	Jack Katoll J. Katoll	74	September 1902	8	1	7	.125	8	6.04	15	8	0	0	67.0	108		5	18	1	0		0	2.01	2.42	0.83	0.67		5.4	1.88	.350	9.94	14.51
2	Ike Butler I. Butler	72	September 1902	10	1	7	.125	9	6.15	10	9	0	0	79.0	120		1	34	1	1		0	1.14	3.87	0.29	0.11		9.6	1.95	.388	8.20	13.67
3	Chick Fraser C. Fraser	66	May 1901	9	4	4	.500	8	5.74	26	6	0	0	69.0	86		2	29	6	1		3	3.39	3.78	0.90	0.26		12.6	1.67	.503	8.61	11.22
4	George Mullin G. Mullin	63	August 1902	10	2	7	.222	9	5.31	18	8	0	0	83.0	111		2	23	1	1		7	1.95	2.49	0.78	0.22		7.3	1.61	.399	6.83	12.04
5	Togie Pittinger T. Pittinger	60	July 1903	9	2	6	.250	7		22	7	0	1	67.2	95		3	25	1	2	306	4	2.93	3.33	0.88	0.40	7.2	8.2	1.77	.361	7.98	12.64
6	Snake Wiltse S. Wiltse	60	September 1902	9	2	6	.250	9	5.61	15	9	0	0	78.2	100		1	22	5	0		4	1.72	2.52	0.68	0.11		6.1	1.55	.313	6.86	11.44
7	Pat Caraway P. Caraway	59	July 1931	14	1	6	.143	6	11.41	10	0	0	1	41.0	73	52	7	26	1	5	223	2	2.20	5.71	0.38	1.54	4.5	11.7	2.41	.369	12.95	16.02
8	Joe McGinnity J. McGinnity	55	September 1901	12	5	7	.417	12	3.47	18	10	1	0	93.1	98	36	1	20	8	0		3	1.74	1.93	0.90	0.10		5.6	1.26	.313	5.30	9.45
9	Nels Potter N. Potter	54	August 1939	12	1	4	.200	5	7.28	17	1	0	0	55.2	86	45	7	25	3	5	275	3	2.75	4.04	0.68	1.13	6.2	9.1	1.99	.354	8.73	13.90
10	Nels Potter N. Potter	54	August 1938	9	1	6	.143	8	7.99	24	4	0	1	56.1	76	50	8	25	2	1	271	0	3.83	3.99	0.96	1.28	8.9	9.2	1.79	.321	8.63	12.14
11	Ray Benge R. Benge	54	July 1930	7	0	5	.000	7	8.66	10	1	0	0	43.2	72	42	6	14	1	0	218	1	2.06	2.89	0.71	1.24	4.6	6.4	1.97	.353	11.13	14.84
12	Harry Howell H. Howell	54	August 1901	10	2	8	.200	10	4.27	15	9	1	0	80.0	98		1	19	4	0		1	1.69	2.14	0.79	0.11		5.4	1.46	.312	6.08	11.03
13	Casey Patten C. Patten	54	July 1901	9	5	4	.556	8	4.19	27	7	1	0	73.0	100	34	0	21	6	1		1	3.33	2.59	1.29	0.00		7.3	1.66	.427	6.66	12.33
14	Elmer Myers E. Myers	53	August 1917	9	1	7	.125	7	8.67	19	4	0	1	45.2	71	44	1	21	0	2	230	3	3.74	4.14	0.90	0.20	8.3	9.1	2.01	.370	10.45	13.99
15	Jack Bracken J. Bracken	53	September 1901	6	1	5	.167	6	8.06	10	6	0	0	48.0	73	43	3	13	6	0	235	2	1.88	2.44	0.77	0.56	4.3	5.5	1.79	.345	9.94	13.69
16	Bob Groom B. Groom	52	May 1911	9	1	5	.167	7	0.36	18	3	0	0	50.0	74		2	20	2	2		5	3.24	3.60	0.90	0.36		8.6	1.88	.379	9.36	13.32
17	Elmer Stricklett E. Stricklett	52	September 1905	7	2	5	.286	7		17	7	1	0	58.0	71		0	28	3	0	262	3	2.64	4.34	0.61	0.00	6.5	10.7	1.71	.332	8.07	11.02
18	Jack Taylor J. Taylor	52	July 1905	8	1	6	.143	7		13	7	0	1	59.0	74		3	21	4	1	262	2	1.98	3.20	0.62	0.46	5.0	8.0	1.61	.321	7.93	11.29
19	Bill Phillips B. Phillips	52	June 1901	7	1	5	.167	6	6.61	21	5	0	0	49.0	79	36	2	18	1	1		2	3.86	3.31	1.17	0.37		9.2	1.98	.503	9.55	14.51
20	Gordon Rhodes G. Rhodes	51	July 1936	8	1	6	.143	7	6.63	11	4	0	0	55.2	87	41	4	15	0	1	263	0	1.78	2.43	0.73	0.65	4.2	5.7	1.83	.356	8.25	14.07
21	Doc Newton D. Newton	51	June 1901	8	3	5	.375	8	3.84	27	8	0	0	72.2	81	31	3	23	7	0	333	4	3.34	2.85	1.17	0.37	8.1	6.9	1.43	.286	6.32	10.03
22	Bill Hart B. Hart	51	May 1901	7	0	7	.000	7	3.90	6	7	0	0	60.0	74		0	27	4	0		3	0.90	4.05	0.22	0.00		9.3	1.68	.291	7.65	11.10
23	Kaiser Wilhelm K. Wilhelm	50	June 1905	8	0	6	.000	6		20	6	0	0	56.0	70		2	18	0	2		3	3.21	2.89	1.11	0.32		7.3	1.57	.330	8.04	11.25
24	Kaiser Wilhelm K. Wilhelm	50	July 1904	9	2	5	.286	7		6	3	0	0	42.1	68		1	16	1	2	210	1	1.28	3.40	0.38	0.21	2.9	7.6	1.98	.360	10.63	14.46
25	Ned Garvin N. Garvin	50	July 1903	9	4	4	.500	9		30	8	0	0	78.0	81		0	10	4	0	320	3	3.46	1.15	3.00	0.00	9.4	3.1	1.17	.293	5.77	9.35