most strikeouts in a season since 1920 by a left handed pitcher

Since 1920, Sandy Koufax has struck out the most hitters by a left-hander in a season, with 382 strikeouts in 1965.

	NAME	SO	SEASON	TM	G	W	L	W%	GS	ERA	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	ERA-	FIP	FIP-	H/9	PRAA
1	Sandy Koufax S. Koufax	382	1965	LAD	43	26	8	.765	41	2.04	27	8	2	335.2	216	76	90	26	71	5	2	4	1,297	11	10.24	1.90	5.38	0.70	29.5	5.5	0.86	.234	2.41	63	1.93	61	5.79	47.9
2	Randy Johnson R. Johnson	372	2001	ARI	35	21	6	.778	34	2.49	3	2	0	249.2	181	69	74	19	71	18	1	2	994	8	13.41	2.56	5.24	0.68	37.4	7.1	1.01	.315	2.67	55	2.12	48	6.52	63.9
3	Randy Johnson R. Johnson	364	1999	ARI	35	17	9	.654	35	2.48	12	2	0	271.2	207	75	86	30	70	9	0	3	1,079	4	12.06	2.32	5.20	0.99	33.7	6.5	1.02	.292	2.85	53	2.75	59	6.86	57.2
4	Randy Johnson R. Johnson	347	2000	ARI	35	19	7	.731	35	2.64	8	3	0	248.2	202	73	89	23	76	6	0	1	1,001	5	12.56	2.75	4.57	0.83	34.7	7.6	1.12	.326	3.22	56	2.53	53	7.31	61.1
5	Randy Johnson R. Johnson	334	2002	ARI	35	24	5	.828	35	2.32	8	4	0	260.0	197	67	78	26	71	13	0	1	1,035	3	11.56	2.46	4.70	0.90	32.3	6.9	1.03	.289	2.70	54	2.65	61	6.82	47
6	Randy Johnson R. Johnson	329	1998	TOT	34	19	11	.633	34	3.28	10	6	0	244.1	203	89	102	23	86	14	0	1	1,014	7	12.12	3.17	3.83	0.85	32.4	8.5	1.18	.320	3.76	72	2.89	65	7.48	42.2
7	Sam McDowell S. McDowell	325	1965	CLE	42	17	11	.607	35	2.18	14	3	4	273.0	178	66	80	9	132	6	5	7	1,116	17	10.71	4.35	2.46	0.30	29.1	11.8	1.14	.262	2.64	63	2.08	58	5.87	45.4
8	Sandy Koufax S. Koufax	317	1966	LAD	41	27	9	.750	41	1.73	27	5	0	323.0	241	62	74	19	77	0	0	4	1,274	7	8.83	2.15	4.12	0.53	24.9	6.0	0.98	.258	2.06	53	2.07	65	6.72	41.8
9	Steve Carlton S. Carlton	310	1972	PHI	41	27	10	.730	41	1.97	30	8	0	346.1	257	76	84	17	87	1	0	8	1,351	8	8.06	2.26	3.56	0.44	22.9	6.4	0.99	.256	2.18	56	2.00	59	6.68	53.5
10	Chris Sale C. Sale	308	2017	BOS	32	17	8	.680	32	2.90	1	0	0	214.1	165	69	73	24	43	8	0	0	851	3	12.93	1.81	7.16	1.01	36.2	5.1	0.97	.301	3.07	63	2.45	56	6.93	45.5
11	Randy Johnson R. Johnson	308	1993	SEA	35	19	8	.704	34	3.24	10	3	1	255.1	185	92	97	22	99	16	1	1	1,043	8	10.86	3.49	3.11	0.78	29.5	9.5	1.11	.273	3.42	74	3.04	70	6.52	36.2
12	Mickey Lolich M. Lolich	308	1971	DET	45	25	14	.641	45	2.92	29	4	0	376.0	336	122	133	36	92	7	0	2	1,538	7	7.37	2.20	3.35	0.86	20.0	6.0	1.14	.274	3.18	83	2.84	78	8.04	32.5
13	Sandy Koufax S. Koufax	306	1963	LAD	40	25	5	.833	40	1.88	20	11	0	311.0	214	65	68	18	58	3	0	7	1,210	6	8.86	1.68	5.28	0.52	25.3	4.8	0.87	.238	1.97	62	1.85	62	6.19	41.9
14	Sam McDowell S. McDowell	304	1970	CLE	39	20	12	.625	39	2.92	19	1	0	305.0	236	99	108	25	131	7	2	10	1,257	17	8.97	3.87	2.32	0.74	24.2	10.4	1.20	.267	3.19	76	3.06	75	6.96	33.8
15	Clayton Kershaw C. Kershaw	301	2015	LAD	33	16	7	.696	33	2.13	4	3	0	232.2	163	55	62	15	42	5	0	1	890	9	11.64	1.62	7.17	0.58	33.8	4.7	0.88	.281	2.40	57	1.98	52	6.31	47.7
16	Vida Blue V. Blue	301	1971	OAK	39	24	8	.750	39	1.82	24	8	0	312.0	209	63	73	19	88	4	0	3	1,207	10	8.68	2.54	3.42	0.55	24.9	7.3	0.95	.239	2.11	56	2.19	66	6.03	41.4
17	Randy Johnson R. Johnson	294	1995	SEA	30	18	2	.900	30	2.48	6	3	0	214.1	159	59	65	12	65	6	0	1	866	5	12.35	2.73	4.52	0.50	33.9	7.5	1.05	.301	2.73	53	2.08	44	6.68	62
18	Randy Johnson R. Johnson	291	1997	SEA	30	20	4	.833	29	2.28	5	2	0	213.0	147	54	60	20	77	10	0	2	850	4	12.30	3.25	3.78	0.85	34.2	9.1	1.05	.281	2.54	50	2.82	62	6.21	41.3
19	Randy Johnson R. Johnson	290	2004	ARI	35	16	14	.533	35	2.60	4	2	0	245.2	177	71	88	18	44	10	0	1	964	3	10.62	1.61	6.59	0.66	30.1	4.6	0.90	.264	3.22	57	2.29	51	6.48	59.7
20	Steve Carlton S. Carlton	286	1982	PHI	38	23	11	.676	38	3.10	19	6	0	295.2	253	102	114	17	86	1	0	5	1,193	9	8.71	2.62	3.33	0.52	24.0	7.2	1.15	.294	3.47	85	2.40	67	7.70	38.3
21	Steve Carlton S. Carlton	286	1980	PHI	38	24	9	.727	38	2.34	13	3	0	304.0	243	79	87	15	90	2	0	12	1,228	17	8.47	2.66	3.18	0.44	23.3	7.3	1.10	.273	2.58	64	2.41	66	7.19	42.3
22	Sam McDowell S. McDowell	283	1968	CLE	38	15	14	.517	37	1.81	11	3	0	269.0	181	54	78	13	110	10	0	9	1,098	7	9.47	3.68	2.57	0.43	25.8	10.0	1.08	.246	2.61	59	2.25	70	6.06	28.3
23	Sam McDowell S. McDowell	279	1969	CLE	39	18	14	.563	38	2.94	18	4	1	285.0	222	93	111	13	102	7	1	9	1,166	14	8.81	3.22	2.74	0.41	23.9	8.7	1.14	.273	3.51	79	2.29	59	7.01	49.5
24	Bob Veale B. Veale	276	1965	PIT	39	17	12	.586	37	2.84	14	7	0	266.0	221	84	98	5	119	7	2	7	1,126	17	9.34	4.03	2.32	0.17	24.5	10.6	1.28	.300	3.32	80	2.11	62	7.48	38.8
25	Steve Carlton S. Carlton	275	1983	PHI	37	15	16	.484	37	3.11	8	3	0	283.2	277	98	117	20	84	3	0	10	1,183	13	8.73	2.67	3.27	0.63	23.2	7.1	1.27	.321	3.71	85	2.64	71	8.79	33.6