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Five hot fantasy baseball waiver wire pickups, streamers, and sleepers for Week 15 (2026). Undervalued hitters outperforming their ownership percentage and should be more widely owned.
Welcome, RotoBallers, to another edition of our Bargain Basement Hitters for Week 15 of the fantasy baseball season. The All-Star break is right around the corner, but fantasy managers should not consider taking a rest yet. There are still many high-impact players on most waiver wires.
This week, we will look at an outfielder in Miami who is showcasing high-end power and a young infielder in Colorado, among others.
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Kyle Karros, 3B, Colorado Rockies
14% rostered (Yahoo)
The former 145th overall pick made his MLB debut in the 2025 season and posted a .226/.308/.277 slash line over his first 43 MLB contests. During this brief cup of coffee, the third baseman hit just one home run with four doubles and a modest 41:15 K:BB.
Karros has spent the entire 2026 season with the major league roster and has begun to turn the corner. Over the first 55 games of the season, Karros showed similar struggles as he did as a rookie, posting an underwhelming .208/.308/.308 line with just three long balls and a mere seven doubles. As a result, many managers in deeper NL-only leagues likely were not considering holding him entering June.
However, since May 31, Karros has looked far more comfortable at the MLB plate. Over his last 33 contests, the third baseman has quite been an elite fantasy option, sporting a .343/.444/.606 line with 10 doubles, four home runs, and a sharp 20:15 K:BB. His 17.1% K% over this stretch was a drastic improvement compared to the 23.8% he held in the previously noted stretch.
Can the UCLA product maintain this pace and become a priority waiver wire pickup for the second half? When looking at his Baseball Savant page, managers can already begin to see the positive side of the argument. Currently, Karros holds a .342 xwOBA and a .258 xBA, both of which are well above average.
Additionally, he has generated a 43.4% hard-hit rate and a stellar 96th-percentile LA Sweet-Spot% (41.3%). While his current near .350 AVG will not be sustainable, he should settle around a .260 AVG, which will keep him on the fantasy radar, especially when paired with his improving K% and hard-hit metrics.
When looking more closely, Karros has shown steady improvement against fastballs (in xwOBA), which is worth noting, as he has seen fastballs 53.2% of the time this season.
Lastly, Karros has generated a 16.3% Pull AIR%, which should continue to bolster his power production, especially when playing in the hitter's paradise of Coors Field.
Given his near-elite walk rate (89th percentile), above-average xBA, and improving K%, Karros should remain a viable corner infielder in all standard leagues and have top-12 upside at 3B in favorable home stands.
Heriberto Hernandez, OF, Miami Marlins
8% rostered
Likely the most intriguing name on this week's column is Miami's Heriberto Hernandez. Hernandez made his MLB debut last summer like Karros but has shown far stronger production, holding a .266/.347/.438 line with 12 doubles and 10 round-trippers over an 87-game stint.
While Hernandez has had a rough start to his 2026 season, carrying a weak .162 AVG and a .468 OPS over his first 26 games, he has since emerged as one of the top power hitters in their lineup. Since May 16 (his last 36 contests), Hernandez has carried a .286/.341/.661 line with a stellar 1.002 OPS, six doubles, and an eye-catching 12 long balls.
Can the second-year slugger sustain this pace?
Currently, Hernandez boasts elite metrics that should put him on the watch list for all fantasy managers. Entering Wednesday's action, Hernandez holds an elite .369 xwOBA (89th percentile), .267 xBA, and a dominant .513 xSLG (92nd percentile). He also posted a 50.7% hard-hit rate (90th percentile) and an average barrel rate of 10.7%.
When looking at his surface-level stats, his .267 xBA is nearly 30 points higher while his xSLG is an additional 40 points higher, suggesting that he was quite unlucky early on and his current production is worth taking seriously.
However, what can drive his power numbers even further is his elite Pull AIR%. While Hernandez has already been impacting the ball hard, as evidenced in his HH% and Barrel%, his 22.1% Pull AIR% allows him to enjoy power binges, like the one he is currently riding.
Lastly, despite his high-end power profile, Hernandez holds a 22.5% K% (44th percentile) and a strong 10.0% walk rate. He has already swiped five bags, and his high walk rate, improving average, and 85th-percentile sprint speed open the door to a near-15-steal season.
His playing time was shaky early on, but given how he has swung the bat, the Marlins will have trouble keeping him on the bench going forward.
Heriberto bleeping Hernandez
Pinch-hit home run in the bottom of the eighth inning to tie this game back, 5-5
12th home run of the season
Exit velo: 110.4 mph
Distance: 422 feet#Marlins pic.twitter.com/VEQzPWLEI8— Kevin Barral (@kevin_barral) July 8, 2026
Nathan Church, OF, St. Louis Cardinals
7% rostered
The other outfielder who has begun to emerge on the fantasy radar is Nathan Church of the St. Louis Cardinals. Since June 9 (since returning from injury), Church has posted a .247/.307/.420 slash line with three doubles, one triple, three home runs, and a stolen base. Before this recent improvement at the dish, the outfielder carried a similar .247 AVG but showed far less power, hitting for a low .390 SLG and .672 OPS.
Can managers trust his recent improvements at the plate?
Unlike Hernandez, Church's current Statcast profile does not suggest as much confidence in his long-term fantasy appeal. Entering Wednesday, Church has generated a modest .286 xwOBA (12th percentile) and a .234 xBA, both well below average.
While he has generated an 8.5% barrel rate, he is impacting the ball at a low 32.2% hard-hit rate and has an average bat speed of 70.1 mph.
However, given that Church has begun to tap into some upside in power over the last month, his "full picture" may not capture the gradual improvements he has made. When looking at the visual below, managers can see that despite his recent power bump, Church's xSLG has actually declined on fastballs and breaking balls.
Additionally, his xwOBA against both fastballs and breaking balls has declined in June and July relative to his early season production in May.
While the 25-year-old should remain reliable as a stolen-base asset, as shown by his 82nd-percentile sprint speed, his weaker on-base skills (5.3% BB%) and inconsistent power will make him difficult for managers to trust.
Those in deeper leagues needing an outfielder with speed and power upside (albeit with a low average) should consider riding the hot hand, but do not expect a one-hit, second-half breakout as we saw with Hernandez.
Victor Bericoto, 1B/OF, San Francisco Giants
5% rostered
Let's turn our attention to a recently promoted prospect in San Francisco. While Victor Bericoto did not draw much attention when he made his MLB debut back on May 22, he has recently begun to make headlines in the Bay Area.
Over his first 23 MLB games, the outfielder/corner infielder has posted a strong .309/.321/.582 line with three doubles, four home runs, a stolen base, and a 13:1 K:BB.
He has been even more impressive in his last 10 games, holding a .378/.395/.703 line with three of these long balls. Is this the start of a potential second-half breakout?
While the sample size is not overly large, Bericoto has impacted the ball quite well in the first taste of MLB action. According to Statcast, the 24-year-old has generated a strong .477 xSLG with a 14.3% barrel rate, 47.6% hard-hit rate, and a 74.1 mph bat speed. While all of these marks put him well above average, there are some concerning components of his profile.
In his brief stint, the 24-year-old has posted a high 27.5% whiff rate, a low .225 xBA, and a .301 xwOBA. He has also only drawn walks 1.8% of the time, which significantly hinders his floor in points formats.
Earlier in the season, Bericoto held a .299/.355/.449 line at Triple-A with five home runs and a 35:15 K:BB. His power upside is a component to continue to monitor, but managers should not expect him to maintain his +.300 AVG given his high whiff tendencies.
The other component of his profile to monitor is his playing time. While he continues to see every day at-bats in left field with Harrison Bader on the IL, once he returns, Bericoto could be the odd man out, or at least kept in a platoon role.
Those in deeper 12+ teams needing power should consider taking a speculative flier on the young outfielder. He has shown enough raw power upside to warrant a waiver-wire pickup, but those needing consistent batting-average assistance should place their FAAB bid accordingly.
Joe Mack, C, Miami Marlins
5% rostered
Rounding out this list will be another Marlin. Joe Mack, the catcher for this week's column, was spotlighted in this piece a few weeks ago but remains under-rostered given his current production. Through his first 46 games in the major leagues, Mack has posted a .248/.310/.428 slash line with seven long balls and a .728 OPS.
However, over his last 19 games, Mack has been producing at a borderline C1 level by fantasy standards. During this noticed stretch, the former top-100 prospect has posted a strong .269/.356/.635 line with a .991 OPS. He has gone deep six times over this recent surge while posting a low 13.6% strikeout rate and a solid 10.1% walk rate.
Can Mack continue this power surge after the All-Star break?
When looking at the visual below, managers can see that Mack has continued to make steady progress against fastballs, which is a very positive sign. So far in July, Mack has posted an elite .389 xwOBA against this pitch type, the highest in a given month.
However, the concern with his profile is his production against the other two pitch types. While he posted a notable xwOBA against breaking balls and offspeed in June, these numbers have taken a massive hit in July (albeit in a small sample). However, given that he saw these marks continue to increase as the season progressed, managers should expect these underlying metrics to slowly bounce back.
When looking at his overall profile, managers can spot a few cracks in his game. His .235 xBA is slightly lower than his surface-level .248 AVG and his .414 xSLG, which is just below his .428 SLG, suggesting some regression could be coming.
However, what has kept his power numbers aloft (and driven his recent surge) is his high-end bat speed and Pull AIR%. Despite only generating a modest 9.2% barrel rate and a low 37.6% hard-hit rate, Mack has continued to hit for power. This is credited to his high-end 74.4 mph average bat speed and a strong 19.3% Pull AIR%.
While regression is expected to show in his box score, those needing a No. 2 catcher who sees stable at-bats and has the potential to put up 15-home-run seasons should consider picking up Mack off the waiver wire.
If you thought Griffin Conine hit a tank last night, watch this.
Joe Mack with his fifth home run of the season, a two-run shot.
Exit velo: 107.5 mph
Distance: 450 feetLongest Marlins home run this season#Marlins lead, 10-1 pic.twitter.com/PgJMYmgC3S
— Kevin Barral (@kevin_barral) July 1, 2026
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