Players · S · Pitcher · 2026

Justin Slaten

Age: 29
B/T: R/R
Height: 6' 4"
Weight: 222 lb
Number: #63

Born: September 15, 1997 in Longview, TX, United States
MLB debut: March 30, 2024
Drafted: 2019, round 3
College: New Mexico

dbWAR: 2.3
IP: 31.1
ERA: 4.60
FIP: 3.04
K/9: 11.2
FIP−: 73

Justin Slaten is a relief pitcher for the Boston Red Sox. In 2026 he struck out 39 batters over 31.1 innings across 36 appearances, going 2-4. His ERA of 4.60 is 10.0% higher than the league average of 4.18 — 17th of 19 on his team, and 357th of 538 among MLB pitchers with 20+ innings. Stripping out defence, his 3.04 FIP suggests he pitched better than his ERA shows. He missed bats on 25.2% of swings (12.8% of every pitch he threw), walked 5.8% of the batters he faced and struck out 28.5%. His 0.6 dbWAR is built from that FIP rather than runs allowed, so it credits him for what he controls and not for the defence behind him.

League context

Percentile among qualified pitchers, 2026.

FIP3.04

K/911.2

WHIP1.37

WAR.6

WAR by season

Pitching

Standard and advanced, by season.


2026	BOS	36	31.1	2	4	0	35	16	39	8	4.60	3.04	1.37	11.2	2.3	110	73	0.6
2025	BOS	36	34.0	2	4	3	27	16	25	10	4.24	3.69	1.09	6.6	2.6	102	89	0.4
2024	BOS	44	55.1	6	2	2	47	18	58	9	2.93	2.61	1.01	9.4	1.5	72	64	1.3

Platoon splits

How left- and right-handed hitters fare against him.

Season

Opponent batting by the side the hitter bats from, 2026. Counted from play-by-play, so totals can differ from the box-score season line by a plate appearance or two.
Split	PA	AB	H	HR	BB	SO	AVG	OBP	SLG	wOBA	K%
vs LHB	71	68	18	2	2	23	.265	.286	.441	.314	32.4%
vs RHB	66	59	17	2	6	16	.288	.354	.390	.335	24.2%

Pitch sequencing

What Justin Slaten throws in each count, and what he follows each pitch with. Select any cell for the breakdown.

ShowBatter

CutterFour-seamSweeperSinkerCurveball

Select a count to see exactly what Justin Slaten throws in it.

Pitch arsenal

What he throws, how hard, how often it misses, and what hitters do with it.

Season


Cutter	41.5%	211	93.6	2,519	52.1%	18.6%	43	.395	1.039
Four-Seam Fastball	25.2%	128	96.6	2,464	50.0%	20.8%	36	.278	.732
Sweeper	17.1%	87	86.1	2,630	40.2%	43.9%	24	.167	.564
Sinker	12.8%	65	97.3	2,379	49.2%	26.5%	18	.167	.377
Curveball	3.3%	17	84.6	2,710	58.8%	44.4%	6	—	—

Justin Slaten's arsenal by usage. Velocity is average release speed in mph, spin in rpm, and whiff rate is misses per swing — the cleanest single measure of whether a pitch beats hitters. BAA and OPS are what hitters did against each pitch, credited to the one that ended the plate appearance, and are left blank under 15 at-bats.

Head to head

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Similar players

Nearest 2026 seasons by command, run prevention and role, on rate statistics rather than totals.

Brandon EisertCWS

ERA: 5.52
FIP: 3.67
SO: 49
WAR: 0.5

Cole SulserTB

ERA: 4.39
FIP: 3.66
SO: 54
WAR: 0.7

Matt FestaCLE

ERA: 3.78
FIP: 3.61
SO: 69
WAR: 0.9

Grant WolframBAL

ERA: 4.30
FIP: 2.66
SO: 61
WAR: 1.2

How these are computed

wOBA uses linear weights measured from this season's own play-by-play rather than published constants, and wRC+ is park-adjusted against that same league. dbWAR is our own open implementation — not fWAR or bWAR — and the full derivation, including its simplifications, is on the methodology page.