Hey, if you're jab pressuring a shield can your opponents usmash you or does the jab interrupt them first? Is it a timing thing? A spacing thing?
Say you jab fox's shield (input on frame 0). Jab1 comes out frame 3. Unstale Jab1 does 3%, so it incurs (3 + 3/3) = 4 frames of hitlag. Jab1 finishes at frame 17 (I couldn't find any IASA frames in testing) ignoring hitlag, so it finishes after 21 frames. I believe you need to crouch at least one frame in order to get another jab1 instead of a jab2, so the second jab1 comes out on frame 25.
Fox takes 6 frames of (shieldstun and hitlag) from jab1 according to the thread / the formula (though it's looking like 7 in my Dolphin testing, probably because I'm an idiot
... if it is actually 7, subtract 1 from each leniency I wrote.) It takes 1 frame to start jumping out of shield, and then upsmash can cancel jumpsquat, taking 7 frames for the hitbox to come out. So that's frame 3 + 6 + 1 + 7 = 17, which is indeed fast enough to hit you. Upsmash does 18% to jab1's 3% or jab2's 7%, so it has priority in the case of a tie; thus he has a 9 frame window to upsmash you.
On the other hand, if you're spaced sufficiently poorly such that shieldgrab would hit, that comes out on frame 3 + 6 + 7 = 16, which is a 9 frame window. I'm not sure how grab vs hitbox priorities work, so this could be +1 frame.
However, if you go for the immediate jab2, that actually starts on frame 12 (really 16 after hitlag), and contrary to what's posted in the hitboxes thread, seems to come out on frame 4, not 5, which is frame 20, so Fox only has a 4 frame window to upsmash oos or 4 (+1?) frame window to shieldgrab here. Of course, jab2 sucks because if they also shield that, they have like a year to punish you for that.
Fox starts his upsmash (hopefully) frame perfectly, though it seems 1 frame late here
Fox hits the upsmash
I didn't test spacing (max distance jab on his shield might?? outrange upsmash oos, though if he just unshields the jab won't hit him at that distance; this is similar to how Samus can jab the edge of Marth's shield, but won't hit him if he drops his shield, so she can't get shieldgrabbed.)