Luis Castillo and Patrick Corbin were tied for losing the most games in 2021, with 16 games.

	NAME	L	SEASON	TM	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	ERA-	FIP	FIP-	H/9	PRAA
1	Luis Castillo L. Castillo	16	2021	CIN	8	.667	33	.333	33	3.98	192	0	0	0	187.2	181	83	94	19	75	7	0	4	803	1	9.21	3.60	2.56	0.91	23.9	9.3	1.36	.318	4.51	90	3.74	84	8.68	14.5
2	Patrick Corbin P. Corbin	16	2021	WSH	9	.640	31	.360	31	5.82	143	0	0	0	171.2	192	111	114	37	60	3	0	2	751	0	7.50	3.15	2.38	1.94	19.0	8.0	1.47	.305	5.98	139	5.40	126	10.07	-21
3	Sandy Alcantara S. Alcantara	15	2021	MIA	9	.625	33	.375	33	3.19	201	1	0	0	205.2	171	73	85	21	50	10	0	2	837	6	8.80	2.19	4.02	0.92	24.0	6.0	1.07	.270	3.72	76	3.41	82	7.48	17.2
4	Cole Irvin C. Irvin	15	2021	OAK	10	.600	32	.400	32	4.24	125	0	0	0	178.1	195	84	94	23	42	9	0	0	768	3	6.31	2.12	2.98	1.16	16.3	5.5	1.33	.302	4.74	103	4.29	104	9.84	-3.2
5	Jake Arrieta J. Arrieta	14	2021	TOT	5	.737	24	.263	24	7.39	83	0	0	0	98.2	131	81	91	24	44	6	0	3	469	3	7.57	4.01	1.89	2.19	17.7	9.4	1.77	.343	8.30	180	6.16	147	11.95	-21.8
6	Matt Harvey M. Harvey	14	2021	BAL	6	.700	28	.300	28	6.27	95	0	0	0	127.2	160	89	96	19	37	5	0	1	582	3	6.70	2.61	2.57	1.34	16.3	6.4	1.54	.331	6.77	142	4.60	101	11.28	-0.5
7	Jorge López J. López	14	2021	BAL	3	.824	33	.176	25	6.07	112	0	0	0	121.2	142	82	83	21	56	10	2	2	555	9	8.28	4.14	2.00	1.55	20.2	10.1	1.63	.340	6.14	138	5.19	115	10.50	-8.1
8	Adbert Alzolay A. Alzolay	13	2021	CHC	5	.722	29	.278	21	4.58	128	0	0	1	125.2	112	64	66	25	34	5	1	2	519	2	9.17	2.44	3.76	1.79	24.7	6.6	1.16	.266	4.73	110	4.64	111	8.02	-6.3
9	Jordan Lyles J. Lyles	13	2021	TEX	10	.565	32	.435	30	5.15	146	0	0	0	180.0	194	103	104	38	56	7	1	0	769	9	7.30	2.80	2.61	1.90	19.0	7.3	1.39	.299	5.20	117	5.33	121	9.70	-17.8
10	Marcus Stroman M. Stroman	13	2021	NYM	10	.565	33	.435	33	3.02	158	0	0	0	179.0	161	60	70	17	44	7	0	2	730	7	7.94	2.21	3.59	0.85	21.6	6.0	1.15	.286	3.52	76	3.49	83	8.09	14.2
11	JT Brubaker	13	2021	PIT	5	.722	24	.278	24	5.36	129	0	0	0	124.1	123	74	75	28	38	9	0	1	538	3	9.34	2.75	3.39	2.03	24.0	7.1	1.29	.284	5.43	126	5.15	121	8.90	-12.6
12	Zach Davies Z. Davies	12	2021	CHC	6	.667	32	.333	32	5.78	114	0	0	0	148.0	162	95	99	25	75	5	0	2	668	0	6.93	4.56	1.52	1.52	17.1	11.2	1.60	.305	6.02	139	5.44	130	9.85	-20.7
13	Mike Foltynewicz M. Foltynewicz	12	2021	TEX	2	.857	28	.143	24	5.44	97	0	0	0	139.0	139	84	86	35	36	9	0	0	586	2	6.28	2.33	2.69	2.27	16.6	6.1	1.26	.254	5.57	123	6.01	136	9.00	-23.9
14	Jon Gray J. Gray	12	2021	COL	8	.600	29	.400	29	4.59	157	0	0	0	149.0	140	76	83	21	58	8	0	2	644	7	9.48	3.50	2.71	1.27	24.4	9.0	1.33	.298	5.01	95	4.22	95	8.46	4
15	Brad Keller B. Keller	12	2021	KCR	8	.600	26	.400	26	5.39	120	0	0	0	133.2	158	80	89	18	64	7	0	1	613	5	8.08	4.31	1.88	1.21	19.6	10.4	1.66	.347	5.99	120	4.71	111	10.64	-7.2
16	Mike Minor M. Minor	12	2021	KCR	8	.600	28	.400	28	5.05	149	0	0	0	158.2	156	89	92	26	41	5	0	0	669	4	8.45	2.33	3.63	1.47	22.3	6.1	1.24	.290	5.22	112	4.28	101	8.85	-1
17	Kolby Allard K. Allard	12	2021	TEX	3	.800	32	.200	17	5.41	104	0	0	0	124.2	128	75	80	29	31	4	3	0	534	4	7.51	2.24	3.35	2.09	19.5	5.8	1.28	.270	5.78	123	5.36	122	9.24	-12.7
18	Tarik Skubal T. Skubal	12	2021	DET	8	.600	31	.400	29	4.34	164	0	0	0	149.1	141	72	76	35	47	6	1	0	634	4	9.88	2.83	3.49	2.11	25.9	7.4	1.26	.277	4.58	100	5.08	120	8.50	-14.2
19	Tyler Anderson T. Anderson	11	2021	TOT	7	.611	31	.389	31	4.53	134	0	0	0	167.0	170	84	87	27	38	1	0	2	703	1	7.22	2.05	3.53	1.46	19.1	5.4	1.25	.284	4.69	108	4.36	104	9.16	-3
20	Yu Darvish Y. Darvish	11	2021	SDP	8	.579	30	.421	30	4.22	199	0	0	0	166.1	138	78	81	28	44	8	0	1	681	9	10.77	2.38	4.52	1.52	29.2	6.5	1.09	.274	4.38	107	3.90	93	7.47	5.6
21	John Gant J. Gant	11	2021	TOT	5	.688	39	.313	21	4.09	92	0	0	0	110.0	95	50	56	10	71	6	4	2	491	3	7.53	5.81	1.30	0.82	18.7	14.5	1.51	.272	4.58	98	4.77	114	7.77	-7.5
22	Mitch Keller M. Keller	11	2021	PIT	5	.688	23	.313	23	6.17	92	0	0	0	100.2	131	69	69	10	49	7	0	1	470	2	8.23	4.38	1.88	0.89	19.6	10.4	1.79	.388	6.17	146	4.29	101	11.71	-0.6
23	Merrill Kelly M. Kelly	11	2021	ARI	7	.611	27	.389	27	4.44	130	0	0	0	158.0	163	78	82	21	41	4	0	3	667	2	7.41	2.34	3.17	1.20	19.5	6.1	1.29	.301	4.67	106	4.10	100	9.28	0
24	Germán Márquez G. Márquez	11	2021	COL	12	.478	32	.522	32	4.40	176	3	1	0	180.0	165	88	92	21	64	4	0	5	756	15	8.80	3.20	2.75	1.05	23.3	8.5	1.27	.293	4.60	91	3.86	87	8.25	11.7
25	Taijuan Walker T. Walker	11	2021	NYM	7	.611	30	.389	29	4.47	146	0	0	0	159.0	133	79	84	26	55	4	0	0	654	5	8.26	3.11	2.65	1.47	22.3	8.4	1.18	.253	4.75	112	4.56	109	7.53	-6.6