Sneaky Fantasy Baseball Waiver Wire Pickups, Buys: Week 4 - Hot Pitchers To Sustain Success?

April 21, 2026

Andy looks at four sneaky fantasy baseball waiver wire pickups for starting pitchers in Week 4 (2026) on hot streaks, and sees if they can sustain their success.

The MLB regular season is in full swing, and we can almost say the first month of action is in the books. Time flies when you're having fun! Fortunately, with another week of data to analyze, we have even more starting pitchers enjoying potential breakout seasons.

This week, we'll spotlight a budding arm in Chicago who has quietly put together a dominant start, and a post-hype top prospect in Cincinnati who is looking worthy of the top selection the Reds made years back.

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Davis Martin, Chicago White Sox

20% Rostered (Yahoo)

One of the most surprising names that I have covered in this column so far is Davis Martin of the White Sox. Martin was not on the fantasy radar in any formats this spring, but has emerged as not only the front-man of this staff but a viable option in all standard leagues. Through 25 innings (four starts), Martin has posted a strong 2.16 ERA, 1.00 WHIP, with a 19:6 K:BB.

However, after removing his three-run season debut against the Miami Marlins, Martin has logged 20 innings, to the tune of a 1.35 ERA and a 0.90 WHIP. Over his last two starts, he has logged at least seven innings in each start and been an "SP1" in back-to-back weeks.

Is this hot start the beginning of a breakout campaign for the former 14th-round pick?

While his face-value marks may suggest this could be true, his underlying marks are far from promising. Per Baseball Savant, Martin has generated a 4.72 xERA with a .278 xBA, both of which place him in the 29th percentile or lower among qualified pitchers. He has also surrendered a loud 92.5 mph average exit velocity with a hefty 52.9% hard-hit rate.

Martin has allowed barrels at an 8.8% rate and groundballs at a low 33.8% rate. The lone promising mark on his profile is his above-average command (6.4% BB%), which should keep his WHIP low and his ERA manageable given that he limits baserunners.

However, when diving deeper into his pitch-mix, we can spot even more glaring signs that suggest Martin is far from a "top" waiver wire pickup this week. Currently, the right-hander relies on five pitchers more than 12.0% of the time and mixes in a sixth pitch (a curveball) at a 9.8% rate.

His four-seamer leads his arsenal at a 24.4% usage rate and has generated a high .315 xwOBA with a .316 BA. However, the .266 xBA suggests this pitch has gotten unlucky despite his impressive start and is becoming a foundation of his pitch mix.

His No. 2 pitch is where the cracks begin to show. His changeup (18.4% usage) has generated a .182 BA with a .237 wOBA, but holds an alarming .370 xBA and a .414 xwOBA under the hood. His cutter (.18.4% usage) has posted a .929 SLG with an .749 xSLG, suggesting it will not fare much better.

The lone positive pitch to note is his sinker (16.4% usage). This pitch has generated a strong .267 xwOBA with a .141 xBA and has emerged as a strong No. 2 fastball to pair with his four-seamer. He has not deployed it consistently this season, but when he does, it is very effective and could help offset his weaker secondaries.

Martin does not have the longest track record or record of success in the majors (4.10 ERA, 1.29 WHIP last season), which suggests this is nothing more than a hot start and that managers should not be quick to trust after this dominant April. While his four-seamer and sinker have been productive, Martin will need to improve his secondaries to sustain this current trajectory.

His underlying metrics suggest regression is looming, and managers should take that into account when adding him off the waiver wire. While he is not a complete fade, he should only be targeted in deeper 12+ team leagues in favorable matchups for the time being.

Spencer Arrighetti, Houston Astros

40% Rostered

The name on this list for those in shallower leagues is Spencer Arrighetti of the Astros. Arrighetti made his MBL debut back in 2024 and was not the most consistent, but flashed enough upside to make him a top breakout pick heading into the 2025 campaign. Over his first 145 innings in the big leagues, Arrighetti struck out 171 hitters while carrying a 4.53 ERA and a 1.41 WHIP.

His 27.1% K% placed him in the 79th percentile, but his shaky 10.3% BB% limited much of his upside.

In 2025, Arrighetti was limited by several injuries, making only seven starts for the Astros and not enjoying much success, posting a 5.35 ERA and 1.42 WHIP, with a 31:20 K:BB over a short 35 1/3 innings. Fortunately, Arrighetti returned to camp in 2026 at full strength and was in the mix to break camp with the MLB roster.

While he fell short in the initial competition, Arrighetti quickly found his footing at Triple-A Sugar Land, which prompted the early promotion. With the top level of the minor leagues, Arrighetti struck out 20 hitters while holding a 1.26 ERA and a 0.77 WHIP over 14 1/3 frames. Following numerous injuries to the Astros rotation, including ace Hunter Brown, Cristian Javier, Cody Bolton, and Tatsuya Imai, Arrighetti was quickly called up and did not disappoint.

In his season debut, Arrighetti immediately put himself back on the fantasy radar, logging six innings of one-run ball against the Rockies. While he walked four hitters, he allowed only three hits and struck out 10 hitters.

In this contest, Arrighetti leaned on his elite curveball, which did most of the work. This pitch was thrown 38.0% of the time and generated a ridiculous 72.7% whiff rate with a .063 xwOBA. While this level of production is not sustainable (especially from the whiff perspective), this pitch was productive back in 2024, and seeing it return to form is a very positive sign.

In his debut campaign, his curveball was just as effective, generating a 42.4% whiff rate with a .211 xwOBA.

Spencer Arrighetti, Nasty 77mph Curveball. 😨 pic.twitter.com/GbVck3dqIL

— Rob Friedman (@PitchingNinja) March 1, 2025

His No. 2 pitch in his 2026 debut was his weeper (17.0% usage), while his four-seamer carried a slightly lower (16.0% usage). The sweeper was very effective in 2024 as a secondary pitch (fourth-most used), generating a 38.6% whiff rate and a .202 xwOBA. In this start, the sweeper carried a lower 18.2% whiff rate, but given its previous success, managers should not be overly concerned.

His four-seamer clocked in at 92.2 mph, which is a 2.0 mph drop from 2024 and generated a .581 xwOBA. While the curveball saw a similar drop in velocity, it was actually even more effective than it has been in the past. Arrighetti will need to rekindle this four-seamer to fully put together a breakout season.

Given that his curveball and sweeper appear to be prime whiff pitchers, Arrighetti has my attention in all standard leagues. Managers should monitor his velocity, as that could be his undoing, but for now, he is a strong buy heading into Week 4. You won't find pitchers who can post a +27.0% K% on the waiver wire often.

Steven Matz, Tampa Bay Rays

30% Rostered

The 34-year-old southpaw began his career as a starter with the Mets but eventually transitioned to a bullpen role once he joined the St. Louis Cardinals. However, with the Rays, Matz has not only secured a spot in their rotation but also performed quite well.

Through four starts (21 2/3 innings), Matz has held a 3.80 ERA, stellar 1.03 WHIP, and a 21:6 K:BB. However, his ERA is a bit clouded by his four-run debut. Removing this outing, Matz has posted a much lower 2.76 ERA with a 0.92 WHIP and a 19:5 K:BB over his last 16 1/3 innings. In two of these games, Matz struck out at least seven hitters and logged more than 15 outs in two as well.

As he has for most of his career, Matz has continued to rely on his typical four pitches, his sinker, changeup, curveball, and slider. His sinker continues to lead the way, carrying a 45.6% usage rate while his changeup slides in as his No. 2, at a 31.2% usage clip. His changeup and slider are distant No. 3 and No. 4 pitches, with usage rates of about 11.8% and 11.5%, respectively.

This season, his sinker has continued to be a modest primary pitch, posting a 19.4% whiff rate, a hefty jump from the 16.4% whiff rate last summer, but it holds a .361 xwOBA. However, the most notable change came in his changeup.

As shown below, the Rays have opted for him to lean much higher on his changeup in years past, making it a near "1B" pitch to his sinker.

This tweak has been effective, especially when looking at his strikeout totals. Through four outings, his changeup has generated an impressive 38.8% whiff rate, which is on pace to be the highest mark of a single season in his career. This pitch has also held its own, generating a .295 xwOBA with a .154 BA (.239 xBA).

Even though his curveball is not being thrown as often, it has been very productive as a No. 3 pitch, posting a .232 xwOBA with a 25.0% whiff rate. In terms of batted-ball metrics, Matz has seen his ground-ball rate drop form 47.7% to 29.8% and seen his fly-ball rate increase only three points (21.5% - 24.6%).

Given his average command and solid strikeout upside, Matz is a strong waiver wire target in all standard leagues in Week 4. While he is not a set-it-and-forget-it starting pitcher, Matz has high-end streaming upside and could emerge as a weekly SP5 if he continues this trajectory, especially while pitching at Tropicana Field.

Rhett Lowder, Cincinnati Reds

20% Rostered

Rounding out this week's column is the former No. 7 overall pick from the 2023 MLB Draft, Rhett Lowder. Lowder joined the Reds out of Wake Forest and was expected to be a frontline ace for this squad. Lowder quickly progressed through the system, making his professional debut in 2024 and debuting with the Reds later that summer.

Over his first stint in Cincinnati, Lowder logged 30 2/3 innings to the tune of a 1.17 ERA and a 1.27 WHIP. He struck out only 22 hitters in this stint and posted a modest 10.9% BB%. However, in 2025, Lowder was limited by several injuries, similar to Arrighetti, and was unable to even take the mound in MLB. He would log only 9 1/3 innings in the system during the entire campaign.

However, following a full offseason, Lowder returned to big-league camp at full strength and has spent the entire 2026 season in the MLB rotation. Over his first four starts, Lowder has logged 23 innings with a solid 3.52 ERA and a 1.11 WHIP. He has continued to show modest strikeout upside, tallying just 15, but has shown much sharper command, allowing walks at a lower 7.4% rate.

Despite this being only his second stint in the majors, Lowder has completely revamped his pitch repertoire. After leaning in his slider and four-seamer in 2024, Lowder has become a primary sinker pitcher in 2026, with his four-seamer being used as his No.3 pitch.

Lowder has thrown his sinker 29.7% of the time, and it has yielded strong results as evidenced by the .211 xwOBA and .135 xBA. However, the .345 xBA and .401 xwOBA for this pitch are looming in the distance.

His No. 2 pitch, his four-seamer (26.3% usage), has not been overly effective (4.27 wOBA), and the .437 xwOBA suggests there is not much room for immediate improvement. Despite this, Lowder has impressive breaking balls that could unlock more strikeout potential.

His No. 3 and No. 4 pitches (slider and changeup) have averaged a 33.5% and 34.5% whiff rate with an .xwOBA under .228. While the whiffs have yet to translate, Lowder totaled 113 punchouts over his first 108 2/3 innings in the Red system in 2024, suggesting there is room to average a strikeout per inning if they continue to grow.

Lowder has also generated a solid 16.7% Pull AIR% with a 29.2% fly-ball rate, which should limit his damage from the long ball pitching in a hitter's paradise. While the strikeout upside has yet to show on the box score, Lowder does have intriguing secondary pitches that could improve as he gets accustomed to the big leagues. His improved command is also an important factor to continue to monitor.

For now, Lowder is a solid streaming/SP5 in all standard formats.

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