This came up in a response I had for someone in the sub struggling with fastballs, so I figure I'd just share it all with you here. Maybe it'll help maybe it won't. Idk man. Hit the [censored] ball.
I made some timing videos for this reason but I'll try and explain it here. Players in this game always time up pitches in a "good" fashion. Meaning when the foot hits the ground and that stride forward begins, is when you want to swing. How early or late during a windup that the hitter starts his leg kick or timing, the better idea you'll have of the pitch. That's why alot of people love a big hitch or leg kick.
You always want to be in the "early - just before the green box/perfect" side of the timing meter. The reason for this is because the game rewards pull hitting with better exit velocity over anything else. A direct result of them nerfing "just late" timing which used to cause better exit velos and launch angles; how we got the phrase "just late be great".
So now that we know we always want to be early or perfect (you'll get more of these as you get better and better), it makes more sense now to "sell" out on fastballs. If I'm struggling, I'll try and be as early as possible on the next fastball thrown, even if I look silly chasing offspeed for a while. Then slowly dial it back, this might even cost me the first couple innings of a game. That's okay, my goal is to consistently get just infront of fastballs, once I'm able to do so fairly reliably, the next goal is to now be a hitter. You may be wondering "how do I just start getting out infront if I'm always late?". Just swing as soon as you see it leave his hand. Like the moment you think it releases from his finger tips. Just do it. Then start dialing back. Too late? Back to Step one. So on and so forth until it works. It's a mechanic, you can do this.
If I know for sure I can be early on a fastball, I can use the same principal to start adjusting my timing down if I see something not a fastball. Because if you're constantly looking for fastballs your brain will begin to recognize when things don't look like a fastball. The brain loves patterns. This is also a great way to warm up before a game. Go into a practice and just get out infront of chapmans fastball for 3-5 min and when you're consistent go play.
Lastly I wanna cover sinkers. The reason they're so nasty is they come out the same way a slider does in this game. Like a very quick hitch up before coming in at the speed of a 102 fastball it seems. Takes time but a more advanced way of attacking that is once you can pull fastballs, you can just tell yourself "if I see any "offspeed" up in the zone (hip or higher) I need swing fast, like a fastball". That'll help you stay out infront of sinkers and drive with power. Yes you'll be a bit open to cutters but if you hit 5 of his 12 sinkers and get yourself 3 homers or some big hits, does it matter that you're 1-7 swings on the cutter?
Hope this helps, happy hitting!
TL;DR: Sit Fastball, be too early and adjust down, be picky later.