Rich Hill was the oldest relief pitcher in 2021. He was 41 years old.

	NAME	AGE	SEASON	TM	G	W	L	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	H/9
1	Rich Hill R. Hill	41	2021	NYM	1	0	0		0	9.00	4	0	0	0	3.0	4	3	3	0	3	0	0	0	17	0	12.00	9.00	1.33	0.00	23.5	17.6	2.33	.400	9.00	12.00
2	Oliver Perez O. Perez	39	2021	CLE	5	0	1	.000	0	0.00	4	0	0	0	3.2	5	0	1	0	1	0	3	1	18	0	9.82	2.45	4.00	0.00	22.2	5.6	1.64	.385	2.45	12.27
3	John Axford J. Axford	38	2021	MIL	1	0	0		0	54.00	0	0	0	0	0.1	2	2	2	0	1	1	0	0	5	0	0.00	27.00	0.00	0.00	0.0	20.0	9.00	.667	54.00	54.00
4	Ervin Santana E. Santana	38	2021	KCR	36	2	1	.667	0	4.55	49	0	0	0	59.1	59	30	31	8	21	2	19	1	252	7	7.43	3.19	2.33	1.21	19.4	8.3	1.35	.297	4.70	8.95
5	Sergio Romo S. Romo	38	2021	OAK	66	1	1	.500	0	4.67	60	0	0	3	61.2	56	32	33	9	21	2	18	2	259	1	8.76	3.06	2.86	1.31	23.2	8.1	1.25	.281	4.82	8.17
6	Darren O'Day D. O'Day	38	2021	NYY	12	0	0		0	3.38	11	0	0	0	10.2	9	4	4	2	4	1	1	0	46	0	9.28	3.38	2.75	1.69	23.9	8.7	1.22	.250	3.38	7.59
7	Zack Greinke Z. Greinke	37	2021	HOU	1	0	0		0	7.71	3	0	0	0	2.1	2	2	2	1	0	0	0	0	9	0	11.57	0.00		3.86	33.3	0.0	0.86	.200	7.71	7.71
8	Jesse Chavez J. Chavez	37	2021	ATL	26	3	1	.750	0	2.03	31	0	0	0	26.2	19	6	7	0	8	0	6	1	105	2	10.46	2.70	3.88	0.00	29.5	7.6	1.01	.288	2.36	6.41
9	Scott Kazmir S. Kazmir	37	2021	SFG	1	0	0		0	18.00	2	0	0	0	1.0	3	2	2	1	1	0	0	0	7	0	18.00	9.00	2.00	9.00	28.6	14.3	4.00	.667	18.00	27.00
10	Joakim Soria J. Soria	37	2021	TOT	41	1	4	.200	0	5.06	40	0	0	6	37.1	39	21	21	6	12	1	20	0	159	2	9.64	2.89	3.33	1.45	25.2	7.5	1.37	.330	5.06	9.40
11	Craig Stammen C. Stammen	37	2021	SDP	63	6	3	.667	0	2.80	78	0	0	1	80.1	66	25	26	13	10	3	4	0	318	3	8.74	1.12	7.80	1.46	24.5	3.1	0.95	.248	2.91	7.39
12	Joe Smith J. Smith	37	2021	TOT	50	4	4	.500	0	4.99	34	0	0	0	39.2	47	22	23	5	8	3	12	2	173	2	7.71	1.82	4.25	1.13	19.7	4.6	1.39	.341	5.22	10.66
13	Brandon Dickson B. Dickson	36	2021	STL	2	0	0		0	13.50	1	0	0	0	2.0	5	3	3	1	0	0	1	0	10	0	4.50	0.00		4.50	10.0	0.0	2.50	.500	13.50	22.50
14	David Robertson D. Robertson	36	2021	TBR	11	0	0		0	4.91	15	0	0	0	11.0	11	6	7	2	3	0	1	0	47	0	12.27	2.45	5.00	1.64	31.9	6.4	1.27	.333	5.73	9.00
15	Justin Turner J. Turner	36	2021	LAD	1	0	0		0	0.00	0	0	0	0	1.0	2	0	0	0	0	0	1	0	5	0	0.00	0.00		0.00	0.0	0.0	2.00	.400	0.00	18.00
16	Tyler Clippard T. Clippard	36	2021	ARI	26	1	1	.500	0	3.20	21	0	0	6	25.1	22	9	12	3	11	3	15	1	111	1	7.46	3.91	1.91	1.07	18.9	9.9	1.30	.260	4.26	7.82
17	Blake Parker B. Parker	36	2021	CLE	47	2	1	.667	0	3.09	37	0	0	0	43.2	43	15	15	5	14	2	13	0	185	1	7.63	2.89	2.64	1.03	20.0	7.6	1.31	.299	3.09	8.86
18	Will Harris W. Harris	36	2021	WSH	8	0	1	.000	0	9.00	9	0	0	0	6.0	7	6	6	1	3	0	2	0	30	0	13.50	4.50	3.00	1.50	30.0	10.0	1.67	.353	9.00	10.50
19	Pedro Strop P. Strop	36	2021	CHC	2	1	0	1.000	0	0.00	3	0	0	0	2.0	2	0	0	0	2	0	0	0	10	0	13.50	9.00	1.50	0.00	30.0	20.0	2.00	.400	0.00	9.00
20	Wade LeBlanc W. LeBlanc	36	2021	TOT	9	0	0		0	4.63	8	0	0	0	11.2	13	6	6	3	1	1	4	0	49	1	6.17	0.77	8.00	2.31	16.3	2.0	1.20	.278	4.63	10.03
21	Brandon Kintzler B. Kintzler	36	2021	PHI	28	2	1	.667	0	6.28	22	0	0	0	28.2	44	20	22	6	8	1	6	2	137	0	6.91	2.51	2.75	1.88	16.1	5.8	1.81	.380	6.91	13.81
22	Ian Kennedy I. Kennedy	36	2021	TOT	55	3	1	.750	0	3.20	62	0	0	26	56.1	45	20	21	12	17	2	44	3	228	0	9.91	2.72	3.65	1.92	27.2	7.5	1.10	.244	3.36	7.19
23	Andrew Miller A. Miller	36	2021	STL	40	0	0		0	4.75	40	0	0	0	36.0	41	19	19	5	16	5	6	1	164	1	10.00	4.00	2.50	1.25	24.4	9.8	1.58	.367	4.75	10.25
24	Josh Tomlin J. Tomlin	36	2021	ATL	35	4	0	1.000	0	6.57	37	0	0	0	49.1	69	36	36	10	5	1	6	0	218	0	6.75	0.91	7.40	1.82	17.0	2.3	1.50	.358	6.57	12.59
25	Tony Watson T. Watson	36	2021	TOT	62	7	4	.636	0	3.92	44	0	0	0	57.1	40	25	26	4	18	0	4	1	225	0	6.91	2.83	2.44	0.63	19.6	8.0	1.01	.226	4.08	6.28