Credit goes to https://psnprofiles.com/guide/9957-mlb-the-show-20-trophy-gu...
but can confirm this is an extremely effective method.
Recommended strategy is to play as the N.L. All Stars against whatever team you like, but the Brewers have a lot of mediocre right handed pitchers, perfect for the stacked lefty squad of the N.L. All Star roster. Playing in Miller Park is also ideal because there is little to no wind influence on the ball, so you'll be mashing bombs left and right, especially given that it's a hitter friendly ball park.
You'll want to play as the away team so that you're guaranteed to bat every inning. It is unclear whether being the home team and having the lead after the top half of the 9th would prevent you from getting the trophy (since you would not bat in the bottom of the 9th), so to be safe, play as the road team and score in all innings 1-9.
Below is a breakdown of the lineup adjustments you'll want to make to maximize your offensive potential with the N.L. All Stars, followed by the sliders to use to your favor to increase the likelihood of hitting home runs on every at-bat.
Ronald Acuna Jr.
Feel free to pitch with whoever you like to strike folks out. Scherzer is always a good choice for strikeouts.
Maximize: Human Contact/Power/Timing/Solid Hits/Starter Stamina/Reliever Stamina/Pitcher Control/Pitcher Consistency/Baserunner Speed/Baserunner Steal Ability
Minimize: CPU Pickoffs/Fielder Run Speed/Fielder Arm Strength Outfield
With this setup, go ahead and launch a game with the Brewers at home against the N.L. All Star lineup as listed above. Select to play in October at 7pm so you can see the ball from the beginning of the game, otherwise the sun shining in center will make pitches invisible and harder to hit. Use Square or Cross to swing, depending on your personal preference which is more successful between power or normal swings. Regardless, nearly every ball you make contact with should go out of the yard provided its timed up remotely close to on time.
With this method, there is still room for a string of RNG fly outs on good/good contacts. It happens. Remain patient, restart, and you'll get there! Also, occasionally they throw Josh Hader in the game late to spoil the fun after demolishing the Brewers bullpen. This happens around the 8th inning, typically up by 20+ runs. If Hader makes an appearance, be patient at the plate and don't be as free-swinging as you can be with the other pitchers. Even so, you can score big time off of him too. And remember, you only need 1+ runs each inning, nothing fancy.
*My first attempt, Hader came in in the 8th after I went up 30-1 and ruined it. My second attempt in order to avoid him, I just bunted and attempted to extend plays to get easy outs after I had scored at least 1 run in the inning. This kept Hader off the mound and got me the trophy! Hope this helps everyone