Jim Whitney has the best slugging percentage by a pitcher in a season, with a slugging percentage of .510 in 1882.

Interpreted as:

highest slg with a minimum of 3.1 PA per team game in a season by a pitcher

	NAME	SLG	SEASON	TM	G	AB	R	H	2B	3B	HR	RBI	BB	HBP	SO	PA	TB	XBH	AVG	OBP	OPS	WRC	WRAA	WOBA	WRC+	BRAA
1	Jim Whitney J. Whitney	.510	1882	BOS	61	251	49	81	18	7	5	48	24		13	275	128	30	.323			65	26	.399	162	25.3
2	Jim Whitney J. Whitney	.433	1883	BSN	96	409	78	115	27	10	5	57	25		29	434	177	42	.281			83	18	.337	121	14.8
3	Charlie Sweeney C. Sweeney	.404	1884	TOT	86	339	55	104	23	2	2	19	21		17	360	137	27	.307			71	18.4	.345	136	19
4	Al Spalding A. Spalding	.373	1876	CWS	66	292	54	91	14	2	0	44	6		3	298	109	16	.312			55	10.8	.324	119	8.4
5	Tony Mullane T. Mullane	.372	1884	TOL	95	352	49	97	19	3	3		33	1		386	131	25	.276	.339	.712	72	15.3	.330	122	12.7
6	Jim Devlin J. Devlin	.369	1876	LOU	68	298	38	94	14	1	0	28	1		11	299	110	15	.315			54	9.3	.318	109	4.2
7	Terry Larkin T. Larkin	.363	1878	CWS	58	226	33	65	9	4	0	32	17		17	243	82	13	.288			42	9	.329	121	7
8	Curry Foley C. Foley	.361	1880	BOS	80	332	44	97	13	2	2	31	8		14	340	120	17	.292			53	9.4	.305	121	9.3
9	Old Hoss Radbourn O. Hoss Radbourn	.352	1883	PRO	89	381	59	108	11	3	3	48	14		16	395	134	17	.283			64	4.8	.301	104	2.5
10	Henry Porter H. Porter	.350	1884	MIL	11	40	3	11	3	0	0		0			40	14	3	.275			6	0.1	.283	-235	-19
11	John Ward J. Ward	.349	1879	PRO	83	364	71	104	9	4	2	41	7		14	371	127	15	.286			58	6.4	.293	112	6.4
12	Charlie Buffinton C. Buffinton	.344	1884	BSN	87	352	48	94	18	3	1	39	16		12	368	121	22	.267			58	4.8	.296	103	1.8
13	Jim Whitney J. Whitney	.337	1881	BOS	75	282	37	72	17	3	0	32	19		18	301	95	20	.255			42	1.7	.297	101	0.6
14	Pud Galvin P. Galvin	.336	1879	BUF	67	265	34	66	11	6	0	27	1		56	266	89	17	.249			35	-1.7	.262	91	-3.6
15	Guy Hecker G. Hecker	.334	1883	LOU	81	332	59	90	6	6	1		12			344	111	13	.271			52	0.4	.288	104	2
16	Mickey Welch M. Welch	.325	1883	NYG	84	320	42	75	13	5	2	30	10		38	330	104	20	.234			43	-6.2	.263	82	-9.6
17	Jim Devlin J. Devlin	.325	1877	LOU	61	268	38	72	6	3	1	27	7		27	275	87	10	.269			39	-1.2	.283	85	-6.3
18	George Bradley G. Bradley	.323	1879	TRO	63	251	36	62	9	5	0	23	1		20	252	81	14	.247			32	-2.8	.256	90	-3.5
19	George Bradley G. Bradley	.321	1876	STL	64	265	29	66	7	6	0	28	3		12	268	85	13	.249			38	-2.4	.266	101	0.2
20	John Coleman J. Coleman	.314	1883	PHN	90	354	33	83	12	8	0	32	15		39	369	111	20	.234			49	-6.7	.263	83	-10
21	Lon Knight L. Knight	.313	1876	PHI	55	240	32	60	9	3	0	24	2		2	242	75	12	.250			33	-2.9	.262	85	-5.5
22	Terry Larkin T. Larkin	.311	1877	HAR	58	228	28	52	6	5	1	18	5		23	233	71	12	.228			28	-6.3	.254	86	-4.8
23	Jim McCormick J. McCormick	.311	1881	CLE	70	309	45	79	9	4	0	26	5		16	314	96	13	.256			37	-5.8	.266	87	-5.6
24	Tony Mullane T. Mullane	.307	1882	LOU	77	303	46	78	13	1	0		13			316	93	14	.257			44	-0.4	.274	103	1.3
25	George Bradley G. Bradley	.304	1877	CWS	55	214	31	52	7	3	0	12	6		19	220	65	10	.243			27	-4.6	.263	79	-7