Babe Ruth had the best on-base percentage in 1921, with an on-base percentage of .512.

Interpreted as:

best obp with a minimum of 3.1 PA per team game by an MLB player 1921

	NAME	OBP	SEASON	TM	G	AB	R	H	2B	3B	HR	RBI	BB	HBP	SO	SB	CS	PA	TB	XBH	SH	AVG	SLG	OPS	WRC	WRAA	WOBA	WRC+	BRAA
1	Babe Ruth B. Ruth	.512	1921	NYY	152	540	177	204	44	16	59	168	145	4	81	17	13	693	457	119	4	.378	.846	1.359	214	127.8	.575	224	118.7
2	Rogers Hornsby R. Hornsby	.458	1921	SLN	154	592	131	235	44	18	21	126	60	7	48	13	13	674	378	83	15	.397	.639	1.097	162	77.5	.489	191	77.7
3	Ty Cobb T. Cobb	.452	1921	DET	128	507	124	197	37	16	12	101	56	3	19	22	15	581	302	65	15	.389	.596	1.048	131	58.2	.471	164	51.2
4	Harry Heilmann H. Heilmann	.444	1921	DET	149	602	114	237	43	14	19	139	53	2	37	2	6	672	365	76	15	.394	.606	1.051	151	67.5	.472	164	59.5
5	Tristram Speaker T. Speaker	.439	1921	CLE	132	506	107	183	52	14	3	75	68	2	12	2	4	588	272	69	12	.362	.538	.977	119	45.8	.444	146	37.3
6	Ken Williams K. Williams	.429	1921	SLA	146	547	115	190	31	7	24	117	74	4	42	20	17	646	307	62	21	.347	.561	.990	133	52.1	.447	146	41.1
7	Wally Schang W. Schang	.428	1921	NYY	134	424	77	134	30	5	6	53	78	5	35	7	4	513	192	41	6	.316	.453	.881	91	26.5	.411	128	19.7
8	Lu Blue L. Blue	.416	1921	DET	153	585	103	180	33	11	5	75	103	5	47	13	17	709	250	49	16	.308	.427	.843	116	27.7	.396	120	19.2
9	Eddie Collins E. Collins	.412	1921	CWS	139	526	79	177	20	10	2	58	66	2	11	12	10	607	223	32	13	.337	.424	.836	97	21.7	.392	117	14.5
10	Joe Sewell J. Sewell	.412	1921	CLE	154	572	101	182	36	12	4	93	80	11	17	7	6	683	254	52	20	.318	.444	.856	114	28.3	.399	120	18.4
11	Ross Youngs R. Youngs	.411	1921	NYG	141	504	90	165	24	16	3	102	71	1	47	21	17	594	230	43	18	.327	.456	.868	100	26	.402	134	25.5
12	George Sisler G. Sisler	.411	1921	SLA	138	582	125	216	38	18	12	104	34	5	27	35	11	635	326	68	14	.371	.560	.971	125	46	.437	140	35.3
13	Jack Fournier J. Fournier	.409	1921	SLN	149	574	103	197	27	9	16	86	56	8	48	20	22	661	290	52	23	.343	.505	.914	120	37.6	.418	145	37.8
14	Harry Hooper H. Hooper	.406	1921	CWS	108	419	74	137	26	5	8	58	55	1	21	13	7	487	197	39	12	.327	.470	.876	83	22.3	.404	125	16.5
15	Ray Grimes R. Grimes	.406	1921	CHC	147	530	91	170	38	6	6	79	70	6	55	5	8	622	238	50	16	.321	.449	.855	103	25	.397	130	23.6
16	Ralph Young R. Young	.406	1921	DET	107	401	70	120	8	3	0	29	69	3	23	11	9	486	134	11	13	.299	.334	.740	66	5.3	.361	99	-0.5
17	Baby Doll Jacobson B. Doll Jacobson	.398	1921	SLA	151	599	90	211	38	14	5	90	42	3	30	8	8	663	292	57	19	.352	.487	.885	113	30.4	.404	121	19.2
18	Jack Tobin J. Tobin	.395	1921	SLA	150	671	132	236	31	18	8	59	45	3	22	7	12	731	327	57	12	.352	.487	.882	124	32.7	.403	120	20.3
19	Max Carey M. Carey	.395	1921	PIT	140	521	85	161	34	4	7	56	70	4	30	37	12	625	224	45	30	.309	.430	.825	97	18.9	.385	122	17.5
20	Austin McHenry A. McHenry	.393	1921	SLN	152	574	92	201	37	8	17	102	38	2	48	10	20	628	305	62	14	.350	.531	.924	114	35.6	.418	145	35.8
21	Larry Gardner L. Gardner	.391	1921	CLE	153	586	101	187	32	14	3	120	65	4	16	3	3	686	256	49	31	.319	.437	.828	106	20	.384	111	10.1
22	Whitey Witt W. Witt	.390	1921	PHA	154	629	100	198	31	11	4	45	77	1	52	16	15	726	263	46	19	.315	.418	.809	108	17.5	.377	105	5.2
23	Dave Bancroft D. Bancroft	.389	1921	NYG	153	606	121	193	26	15	6	67	66	4	23	17	10	698	267	47	22	.318	.441	.830	108	20.5	.384	122	19.9
24	Tilly Walker T. Walker	.389	1921	PHA	142	556	89	169	32	5	23	101	73	4	41	3	5	640	280	60	7	.304	.504	.892	110	30.2	.406	122	19.3
25	Mike Menosky M. Menosky	.388	1921	BSA	133	477	77	143	18	5	3	45	60	9	45	12	6	565	180	26	19	.300	.377	.766	78	7.6	.364	103	2.2