50 pitchers are tied for the best K/9 by a relief pitcher in a season, with 27.00 per nine innings. The first three are Jayvien Sandridge this season and Will Warren and Evan Justice in 2024.

	NAME	K/9	SEASON	TM	G	W	L	GS	ERA	SO	CG	SHO	SV	IP	H	ER	R	HR	BB	HBP	GF	IBB	TBF	WP	BB/9	K/BB	HR/9	K%	BB%	WHIP	BABIP	RA	H/9
1	Jayvien Sandridge J. Sandridge	27.00	2025	NYY	1	0	0	0	27.00	2	0	0	0	0.2	1	2	2	1	2	1	0	0	6	0	27.00	1.00	13.50	33.3	33.3	4.50		27.00	13.50
2	Will Warren W. Warren	27.00	2024	NYY	1	0	0	0	27.00	3	0	0	0	1.0	2	3	3	1	1	0	1	0	6	0	9.00	3.00	9.00	50.0	16.7	3.00	1.000	27.00	18.00
3	Evan Justice E. Justice	27.00	2024	COL	1	0	0	0	0.00	1	0	0	0	0.1	0	0	0	0	1	0	1	0	2	0	27.00	1.00	0.00	50.0	50.0	3.00		0.00	0.00
4	Clayton Andrews C. Andrews	27.00	2024	NYY	1	0	0	0	27.00	1	0	0	0	0.1	1	1	1	1	0	1	0	0	3	0	0.00		27.00	33.3	0.0	3.00		27.00	27.00
5	Romy González R. González	27.00	2021	CWS	1	0	0	0	0.00	1	0	0	0	0.1	0	0	0	0	0	0	1	0	1	0	0.00		0.00	100.0	0.0	0.00		0.00	0.00
6	Kevin Quackenbush K. Quackenbush	27.00	2021	LAD	1	0	0	0	27.00	1	0	0	0	0.1	3	1	1	0	0	0	0	0	4	0	0.00		0.00	25.0	0.0	9.00	1.000	27.00	81.00
7	Nick Maton N. Maton	27.00	2021	PHI	1	0	0	0	0.00	1	0	0	0	0.1	0	0	0	0	0	0	1	0	1	0	0.00		0.00	100.0	0.0	0.00		0.00	0.00
8	Mike Freeman M. Freeman	27.00	2021	CIN	1	0	0	0	0.00	1	0	0	0	0.1	0	0	0	0	0	0	1	0	1	0	0.00		0.00	100.0	0.0	0.00		0.00	0.00
9	Wil Crowe W. Crowe	27.00	2021	PIT	1	0	0	0	13.50	2	0	0	0	0.2	1	1	1	0	2	0	0	0	5	2	27.00	1.00	0.00	40.0	40.0	4.50	1.000	13.50	13.50
10	Chaz Roe C. Roe	27.00	2021	TBR	1	0	0	0	27.00	2	0	0	0	0.2	1	2	2	0	1	0	0	0	4	0	13.50	2.00	0.00	50.0	25.0	3.00	1.000	27.00	13.50
11	Freddy Peralta F. Peralta	27.00	2021	MIL	1	0	0	0	0.00	6	0	0	0	2.0	2	0	0	0	3	0	0	0	11	0	13.50	2.00	0.00	54.5	27.3	2.50	1.000	0.00	9.00
12	Mike Brosseau M. Brosseau	27.00	2020	TBR	1	0	0	0	0.00	1	0	0	0	0.1	0	0	0	0	0	0	1	0	1	0	0.00		0.00	100.0	0.0	0.00		0.00	0.00
13	Jeremy Beasley J. Beasley	27.00	2020	ARI	1	0	0	0	0.00	1	0	0	0	0.1	2	0	0	0	0	0	1	0	3	0	0.00		0.00	33.3	0.0	6.00	1.000	0.00	54.00
14	Tommy Kahnle T. Kahnle	27.00	2020	NYY	1	0	0	0	0.00	3	0	0	0	1.0	1	0	0	0	1	0	0	1	6	0	9.00	3.00	0.00	50.0	16.7	2.00	.500	0.00	9.00
15	Dellin Betances D. Betances	27.00	2019	NYY	1	0	0	0	0.00	2	0	0	0	0.2	0	0	0	0	0	0	0	0	2	0	0.00		0.00	100.0	0.0	0.00		0.00	0.00
16	José Castillo J. Castillo	27.00	2019	SDP	1	0	0	0	0.00	2	0	0	0	0.2	0	0	0	0	1	1	0	0	4	1	13.50	2.00	0.00	50.0	25.0	1.50		0.00	0.00
17	Asher Wojciechowski A. Wojciechowski	27.00	2019	BAL	1	0	0	0	0.00	2	0	0	0	0.2	1	0	0	0	0	0	0	0	3	1	0.00		0.00	66.7	0.0	1.50	1.000	0.00	13.50
18	Jedd Gyorko J. Gyorko	27.00	2019	STL	1	0	0	0	0.00	1	0	0	0	0.1	0	0	0	0	0	0	1	0	1	0	0.00		0.00	100.0	0.0	0.00		0.00	0.00
19	Austen Williams A. Williams	27.00	2019	WSH	2	0	0	0	162.00	1	0	0	0	0.1	5	6	6	2	1	0	0	0	7	0	27.00	1.00	54.00	14.3	14.3	18.00	1.000	162.00	135.00
20	Adrian Sampson A. Sampson	27.00	2018	TEX	1	0	0	0	54.00	1	0	0	0	0.1	4	2	3	1	0	0	0	0	6	0	0.00		27.00	16.7	0.0	12.00	.750	81.00	108.00
21	Danny Valencia D. Valencia	27.00	2018	BAL	1	0	0	0	0.00	1	0	0	0	0.1	0	0	0	0	0	0	1	0	1	0	0.00		0.00	100.0	0.0	0.00		0.00	0.00
22	Jeremy Bleich J. Bleich	27.00	2018	OAK	2	0	0	0	54.00	1	0	0	0	0.1	2	2	2	0	0	1	0	0	4	0	0.00		0.00	25.0	0.0	6.00	1.000	54.00	54.00
23	Roenis Elias R. Elias	27.00	2017	BOS	1	0	0	0	0.00	1	0	0	0	0.1	0	0	0	0	1	0	1	0	2	0	27.00	1.00	0.00	50.0	50.0	3.00		0.00	0.00
24	Damien Magnifico D. Magnifico	27.00	2017	LAA	1	0	0	0	0.00	1	0	0	0	0.1	0	0	0	0	2	0	0	0	3	0	54.00	0.50	0.00	33.3	66.7	6.00		0.00	0.00
25	William Cuevas W. Cuevas	27.00	2017	DET	1	0	0	0	108.00	1	0	0	0	0.1	3	4	4	0	0	1	0	0	5	0	0.00		0.00	20.0	0.0	9.00	1.000	108.00	81.00