I really struggled with the Midline read for ages, finally figured it out recently and it's still hard to articulate it. Apparently, there's not a specific animation the DT does, unlike the way the Read Option's keyed defender has his universal stutter-step to signal a Give read. (Warning, very long-winded explanation of the Midline read incoming.)
Like you probably already know, the Midline read is 100% just a regular zone read (if the DT
chases, the QB keeps and
replaces [the DT], and if the DT
remains, the QB
hands off the reins [to the HB].) I was so terrible at making the read at first that I started thinking maybe EA just coded the read like the Inverted Veer (DE chases = QB hands off). Which was a mistake & led to the frustration that made me just give up on the play for so long
I wish I could specifically articulate what to look for, but I feel very confident that if you take it into Practice mode you can pick it up pretty quick -- this is how it was explained to me, and the lightbulb moment came quickly. I still misread it sometimes, but it doesn't bother me because it's always A) because I just make the completely wrong read, or B) it was a murky read, and I got greedy and kept it instead of just handing off & settling for the tiny 1-yard loss/gain. But it's actually become a really nice play to have once the CPU D starts overplaying the Read Option.
I think the best way to practice it would be against a 4-3 Over/Under in Practice mode, with the 3-tech as the keyed defender (so shading the RG in a 4-3 Over, or shading the LG in a 4-3 Under). I'd just put the defense in a Cover 2 Man so there's no run blitz and you have the numbers advantage with blockers (more space, easier to see what's happening on each read, etc.)
The only way I have to describe it is
"hesitation" -- if the DT shows any hesitation, it's a handoff. If he books it straight for the HB, the QB keeps & replaces the DT (of course, the whole issue is that the angle he follows makes it hard to tell if he's staying or going, unlike the much wider angle of the keyed defender in the Read Option -- so you look for the hesitation instead.)
One of the hardest aspects for me was that both outcomes seemed so unintuitive --
it can go against your instinct to keep with the QB when an unblocked DT is charging right at the QB/HB mesh, but that's of course the clearest possible Keep read with the Midline. Your instincts scream "hand it off" but really you just want to use the DT's momentum against him and scurry right past his big ***. You'll be crossing the LoS by the time he's even managed to turn his shoulders back around.
OTOH,
it seems equally unintuitive to hand the ball off when an unblocked DT is 3-4 yards away staring right at you, but in that case you're going the other way with the HB and catching the DT completely flat-footed.
For me, the big advantage of the Midline has been that when it's a murky read, the Give read /usually/ ends up being the correct read anyway, not just the safer bet. So having the good habit of "murky read = just hand it off" is a big help.
Of course, you don't need the Midline, just sticking to the Read Option is obviously more than good enough, haha. Just thought I'd share how I finally figured out the read since it might help somebody reading the thread way down the road.
Where it gets tricky though is that it works better against some fronts and worse against others. Which of course is true of all running plays, options or not, but the fronts that EA's Midline works against aren't necessarily the same as the ones the real-life Midline works against (I've had decent success with Midline against odd 0-tech fronts, which is completely inexplicable lol, but EA can only take their blocking physics so deep I guess).
But in theory, the Midline is best run to 2-tech or 3-tech interior linemen and not so good against an Odd/Stack front.
One little thing to note is that I play with JoshC's 50-threshold sliders, so all of these points might be completely invalid with some of the more extreme slider sets. Good luck to anyone that tries to figure out the Midline though, once it clicks it will really click, I can promise that from my own experience.