There’s a weird thing in a lot of American sports about not rubbing it in if you’re winning a game massively, so in the NFL or NBA, if a team is well ahead in the 4th quarter, they’ll sub off all their best players and kind of go easy on the other team.
I think this must be the baseball equivalent, the hitters team are seven runs up in the penultimate inning, so they don’t need to score more, and as its a 3-0 pitch, he loses nothing if he doesn’t swing at it and just takes a strike, or he could just not go full pelt at it and not hit it out the park.
I think it’s a weird thing to get upset about though. Maybe don’t throw a fastball down the middle in that situation?