Only five games remain before the Chicago Cubs close out what’s been an excellent first half. After two straight disappointing seasons with 83 wins, they’ve surpassed all expectations so far with a 54-37 record, powered by the league’s third-best offense by wRC+ (118) and a bullpen that has morphed into a shutdown unit. The addition of Kyle Tucker was a game-changer, but they wouldn’t be where they are without a lot of players taking steps forward.
Heading into the back half of the season, there’s a lot to be encouraged by, especially with Jed Hoyer and company actively scouring the market for rotation upgrades and more. That said, the Milwaukee Brewers are still red hot and only 2.5 games back with the Cardinals and Reds lurking behind. To finally win the division again and be a real threat in the playoffs, they’ll have to keep up the pace down the stretch. For some of their key contributors, that seems very doable, but there are a few players who may be due for some regression as the year winds on.
Ahead of the All-Star break, let’s look at two key position players and three pitchers to see whose performances are sustainable and whose are not.
Sustainable: Pete Crow-Armstrong
No player has defined the 2025 Cubs more than Pete Crow-Armstrong. The center fielder and former top prospect has ascended to superstardom, slashing .272/.309/.550 with a 137 wRC+ and 27 stolen bases in 376 plate appearances. Most shocking, however, is his sudden discovery of a power stroke, with 23 home runs so far to place him second on the team behind only his bash brother, Seiya Suzuki. Coupled with his eye-popping outfield defense, it’s been enough to make him the most valuable player in the National League with 4.8 fWAR and earn him a starting spot in the All-Star Game.
While PCA has had minor slumps, the underlying numbers don’t suggest much regression either. His .298 BABIP is in line with the league average, and his .364 wOBA is only slightly better than his expected .354 mark. While his first percentile chase rate needs improvement and he’s only squaring up about 23 percent of balls, he still has an 85th percentile barrel rate, expected batting average of .260, and expected slugging percentage of .530.
On top of everything, his 97th percentile sprint speed makes taking extra bases and beating grounders so much easier. Simply put, his rapid improvement certainly looks real.
Sustainable: Michael Busch
Alongside Crow-Armstrong, Tucker, and Suzuki, Michael Busch has helped transform the middle of the Cubs lineup into something worth fearing with a .297/.382/.562 slash line and 166 wRC+. He’s improved on his already solid 118 wRC+ rookie year in nearly every way, striking out at a much better 22.6 percent rate in addition to posting offensive numbers that place him in the top five of all of baseball behind Shohei Ohtani (168 wRC+). That big bat comes attached to a first baseman who is an overall positive defender with two defensive runs saved.
The stark difference between 2024 and 2025 becomes apparent when looking at his Baseball Savant page. Virtually all of his expected stats have exploded into bright red, along with his hard hit rate, barrel rate, and launch angle sweet spot percentage. Although he’s been protected against lefties, whom he only has a 79 wRC+ against, he’s even started to find success there of late, punishing southpaw Matthew Liberatore with two extra-base hits, including a home run, on July 5.
After being given the time to develop, Busch is making better swing decisions and hitting the ball with more authority than ever. When your expected batting average and slugging percentage are .281 and .576, you’re having a monster season, and there’s little reason to expect significant regression.
Fool’s Gold: Chris Flexen
It can’t be stated enough how vital Chris Flexen has been to the resurgent bullpen. Along with Drew Pomeranz, he’s been one of the big minor league signing surprises, racking up a 0.83 ERA in 32 1/3 innings. Thanks to a career-low 2.20 walks per nine, the Cubs have been able to rely on him either to cover critical late innings or eat up chunks of the game on days when the starter doesn’t go deep.
However, the numbers suggest he’s getting more than a little lucky. His xERA is at 3.25, with a FIP and xFIP at 3.57 and 4.50, respectively, suggesting some serious regression is coming. That’s backed up by an unsustainable .198 BABIP, 5.3 percent home run to fly ball rate, and 95.2 percent left on base rate. He’s also not striking anybody out with a career-low strikeouts per nine of 4.68. He was never going to keep his ERA that low, but if the winds shift and balls start landing, expect that number to balloon concerningly fast.
Fool’s Gold: Colin Rea
An early season-ending injury to Justin Steele threatened to derail the Cubs before their season was a third of the way through, if not for Colin Rea. The team’s other free agent starter signing hasn’t been quite as successful as Matthew Boyd, posting a 4.13 ERA in 85 innings, but his early-season success was vital to their survival. Alas, his stellar April appears to have been a mirage with more and more red flags arising as the months passed.
In both May and June, Rea posted an ERA over five and had three starts with six or more runs given up. In that time, the underlying numbers have gotten ugly with an expected batting average (.290) and slugging percentage (.489) in the bottom 10 percent of baseball. His 2.22 walks per nine is nice, but not when paired with 6.35 strikeouts per nine, a 4.81 FIP, and an average exit velocity allowed of 90.8 mph. By the quality of contact he’s giving up and the bats he’s not missing, he’s earned that xERA of 5.01, and that’s not going to cut it on a team with playoff ambitions.
Sustainable: Brad Keller
In a year full of unexpected bullpen success stories, Brad Keller is perhaps the most heartening because his results are among the most sustainable. He came into spring training a transformed pitcher, with a 97 mph fastball that blew everyone away. Since then, he’s only continued to run with the set-up job, posting a 2.88 ERA and 3.11 FIP and landing in the center of Craig Counsell’s circle of trust.
Although he most recently had a disastrous, game-altering outing against St. Louis, don’t let that fool you about his abilities. Keller ranks among the best pitchers in baseball in limiting hard contact, as indicated by his 96th percentile average exit velocity (86 mph) and hard hit rate (31 percent). He’s also getting groundballs at an elite rate of 61.1 percent, which plays very well with the Cubs’ infield defense. New changes to his arsenal have also prioritized his deadly sweeper against righties, all while his fastball has proven to be much more effective at limiting batting average.
Everything adds up to Keller being mostly in line with his 2.96 xERA. This is about the best he’s looked in his career, and while he’s not necessarily striking out batters at an elite rate, he does enough else well that it shouldn’t tank his results.