Mirror Report: Brendan McKay

Two-way player Brendan McKay (4th overall selection in the 2017 Amature Draft) of the Tampa Bay Rays pitched 49 innings last year and posted an 0.8 WAR backed by a 4.03 FIP with a 3.5 K/BB-rate.


McKay operates with a four-seam fastball, a classic curveball, a traditional cutter, and a rarely-used changeup. For the purpose of this research, we are going to ignore McKay’s cutter and changeup.

McKay’s four-seam fastball is thrown with an 11:10 average spin direction under a gyro degree of -8 (or, roughly 99% Magnus/Spin efficiency). This makes the pitch almost pure backspin with a good amount of run (5.3″) and lift (9.3″). His classic curveball typically holds a spin direction of 4:30 and is 38% gyro spin (or, 62% Magnus/Spin efficiency) with balanced sweep and depth.

McKay generally locates his fastball arm-side middle-in and tends to keep the pitch higher in the zone, which is good as hitters tend to be less-successful with fastballs up in the zone.

Hitters produced a .328 wOBA against McKay’s four-seamer in 2019. Trouble occurs when he located low in the zone, which he didn’t do often but almost never produced desirable results. His SwStr% wasn’t bad at 10% with the majority attributed to high fastballs.

McKay usually keeps his curveball down and in glove-side with a disconcerting amount landing in the middle of the zone.

McKay’s curveball was hit pretty well when he was unable to go low in the zone; hitters produced a .310 wOBA with just a 12.6% SwStr-rate.

McKay’s Command+ mark of 100 demonstrates he has the ability to consistently locate while his K/BB rate shows good control though his walk rate could use some improvement.


McKay has a weapon built into his arsenal design- mirrored fastball and curveball trajectories. For those of you unfamiliar with pitch mirroring, take a look at this article I wrote for Fangraphs a few months ago.

Here’s a visual example of how McKay’s four-seamer and curveball can work together, using his typical locations for each:

Here’s a look at both using BaseballCloud‘s new BallR tool:

Notice that while the designed spin doesn’t mirror McKay still is able to create ‘repelling’ horizontal and vertical movement.

Furthermore, McKay had a nearly identical release point for both the fastball and curveball though he struggled to produce consistent, effective tunneling action with them (tool low w FB, too high with CB).

To elaborate further on how these two pitches are designed to work off each other in a desirable manner, take a look at McKay’s short-form movement chart:

Upon discovering this, I decided to inspect McKay’s performance when he challenged hitters with a FF>CU or CU>FF sequence. I looked over each outing for McKay in 2019 and broke each at-bat with a fastball/curveball sequence into a mirrored and non-mirrored categories. I then inspected how many had beneficial (strikes, fouls, outs) versus detrimental outcomes (ball, walk, hit).

For the mirrored sequences, I verified that there was at least some semblance of a tunnel using Baseball Prospectus’ Batter vs Pitcher matchup tool and moved any of those that the hitter could clearly differentiate (as a FB or CU) into the non-mirrored group; the concept of mirroring could be rendered useless if the hitter can easily tell which pitch is which.


The findings were not overwhelming but do show a decent benefit of McKay utilizing his FB/CU sequences in their most effective form.

McKay threw a total of 115 FB>CB/CB>FB sequences through 15 appearances (two outings in the ALCS). Of those 115, 32% (37 total) were identified as mirrored movement. Of those 37, 17 (69%) resulted in beneficial outcomes. Ten of those 37 mirrored sequence outcomes resulted in outs (19%) with just two resulting in hits and/or runs (4%).

As for the 78 (or 68%) non-mirrored sequences, McKay produced 50 beneficial outcomes (61%). Outs were produced in 23% (29 total) of those 78 non-mirrored sequences while 12% of the non-mirrors (15 total) yielded hits and/or runs.

So McKay generally gets better results when he can mirror his fastball and curveball movement (out of a tunnel). He created more beneficial outcomes (69% versus 61%) and gave up less hits/runs (4% versus 12%) though McKay did induce outs at a higher rate with his non-mirrored sequences (23% versus 19%).

McKay should consider building a pitching strategy around his ability to create mirrored movement (as well tighter tunnels) with his four-seam and curveball; he has the command ability to do so. While it’s not advisable to run this attack against the majority of hitters he faced (constant FB>CB/CB>FB would be too predictable), discretion should be used depending on leverage or game circumstance.