MLB The Show 21

After testing this awhile with various difficulties, players and pitching setups the easiest I got this is while playing Retro mode in less than 10 minutes.

I uploaded the sliders for this so that you can download from the vault if you don't want to do it manually.
Click on the create icon on the main menu, then vaults.
Press to search then type in PitchcollectorTA and search again.
Press to go to sliders tab and download it(should be the only one with my GT).
Now back on main menu go to settings>file management>load>sliders and load the sliders you saved.

To do sliders manually:
On the main menu top right corner click on settings>settings>gameplay>change hitting difficulty to beginner then to general settings and change gameplay to casual. Also, make sure you turn off dynamic difficulty.

Now go back and click on sliders instead of settings. You want to adjust these all the way to the left:
Human timing
Human solid hits
CPU pitcher control
CPU strike frequency
CPU pitcher consistency
All pitch speeds

Now these all the way to the right:
Human foul frequency
Human Contact
Wind

Game mode
Go intro Retro mode and have your team as away so you can bat first. Only thing that matters is you have hitters with good contact(most teams have this) and an opposing pitcher who's main pitch is a 4 seam fastball or curve.
So I choose Dodgers since a few of their hitters have the 20/20 perk which means they rarely miss a ball while swinging early or late plus they have good contact.
Alot of people in the comments are having more success with Corey Seager on the Dodgers for this so you can adjust lineup to have him batting first before starting the game.

In Retro mode you simply press to pitch or hit. Do not swing while at bat, let the CPU pitch. If you're lucky, it'll end up at 3-2 count and you just need to foul off 5 balls. If you happen to get 2 strikes before a 3-2 count, try swinging late or early at pitches inside(close to the batter) and hitting foul balls. It may take a little to get used to timing for a foul ball but the game moves fast. Unfortunately, you can't change the camera angles in this mode.