The one headliner the Pirates must avoid in a Mitch Keller trade

The Pittsburgh Pirates could move right-hander Mitch Keller at the trade deadline, regardless of how poor of a decision that may be. One team reportedly interested in Keller is the Chicago Cubs, and if Bob Nightengale’s reporting is accurate, they are willing to go to great lengths to acquire Keller. The Cubs are reportedly open to offering up top outfield prospect Owen Caissie. On the surface, Caissie may look like the sort of batter the Pirates need, but there are way too many red flags to make this an acceptable return for anyone, especially Mitch Keller.

Caissie is batting .278/.377/.563 with a .409 wOBA and 138 wRC+ over 353 plate appearances for the Chicago Cubs' Triple-A affiliate. On the surface, this looks like the sort of batter the Pirates’ system needs. Caissie has awe-inspiring power, something they don't have enough of right now. He already has 20 home runs on the season with a .285 isolated slugging percentage. Caissie also has a 91.9 MPH exit velocity and 17.9% barrel rate.

But these strong numbers don’t show the massive issues in Caissie’s game. The simplest is that Caissie struggles against left-handed pitching. Caissie has a .208/.337/.377 triple-slash with a .322 wOBA against same-handed hurlers. He struggles to make contact, with a 28% whiff rate, and when he does hit the ball, he has only produced an 88.8 MPH exit velocity and 6.3% barrel rate. His xwOBA is just .278 when going up against a southpaw. Even though he has a .396 xwOBA when facing right-handers, there are still question marks about his game because of his 30.3% whiff rate.

If that were the only red flag, then there wouldn’t be much of an issue, but he also struggles badly against good velocity. Against pitches at 97+ MPH, Caissie is only batting .250 with a .333 slugging percentage and a horrible .215 xwOBA. For reference, the average xwOBA on 97+ MPH pitches at Triple-A is .295, a whole 80 points better than Caissie. His whiff rate is only 12%, but he isn’t even making good contact either, with an 83 MPH exit velocity, and zero percent barrel percentage.

Breaking pitches give Caissie a lot of problems. His .225 batting average, .434 slugging percentage, and .312 xwOBA may not look outright horrible, but he has a 38.1% whiff rate against breakers. The average is 32.1%. Caissie may be making good contact with a 91.1 MPH exit velocity and 15.2% barrel rate, but he’s not doing significantly better overall than the average Triple-A batter against breaking pitches. His whiff percentage is the 34th highest among Triple-A hitters who have seen at least 1,000 total pitches this season.

Owen Caissie's red flags are too big for the Pirates to ignore.

At least Caissie does well against offspeed stuff, with a .323 average, .710 slugging percentage, and .397 xwOBA. But again, we are still talking about a batter who whiffs over a third of the time. That’s about average for Triple-A at 33.2, but still poor overall. Offspeed stuff in what Baseball Savant considers the "shadow of the zone" has gotten Caissie to whiff 37.3% of the time. 

Caissie’s .300 batting average and .450 slugging percentage on fastballs away in the shadow of the zone don’t tell the whole story. He still has a sub-.300 xwOBA at .284, and a whiff rate of 32.6%. The average xwOBA and whiff rate on away fastballs for left-handed batters in the shadow of the zone are .314 and 27.6%, respectively. 

A major league team has infinitely more resources than a blogger with a half hour of digging around on Baseball Savant has. If I can find these, then any Major League team should see the same issues. These red flags are way too big for the Pirates, who have already struggled to develop hitting, to overlook. Caissie struggles against lefties, he struggles against good velocity, and he struggles to make contact against breaking pitches. Trying to hit fastballs away gives him trouble, and he struggles to make contact on offspeed pitches that aren't in the heart of the zone. These are totally issues that will get exploited by Major League pitchers against Caissie.

If the Pirates are going to make a move for a young slugging outfielder, Owen Caissie should be at the very bottom of their list.