The trouble with using it for offside is that the system is not fit for purpose except to show a failure to flag a clear and obvious offside. So use it for that and only that. Tell the liners not to be twitchy and that they'll be fired if they stick the flag too soon. That gives a slight advantage to the attacker. If they don't flag a clear offside, no problem just stick up the picture on the screen after the goal and disallow it. Nobody will complain. If they have to start fiddling about with the VCR, forget it, goal stands. Again nobody will complain because we can't see that well. Which brings me to the point that they seem to have overlooked or decided not to mention. To guarantee a picture of the foot in contact with the ball, you'd need to use something that doesn't exist afaik. A hi-speed camera 1000fps with an automatic zoom lens. There's presumably never been a market for them since if you want to do crash-testing or check out your latest armour-piercing shell, you just set the camera up and retire to the control booth.
Banging on about 50fps is irrelevant because the HD moving picture may well be lovely (I don't know I haven't got that TV) but your brain is joining up the digital dots just as it does with old-fashioned film. So, although I see David Silva passing the ball in one flowing seamless (brilliant) motion, the image that shows David actually first touching the ball simply may not exist. In fact, if we have a series of still images taken every 20 ms (50 fps), and the scientifically proven time of contact lasts for 8 ms (the middle of the range), there may not exist a picture of Merlin's foot in contact with the ball at any stage. God help us at 25 fps. That's why it goes blurry in my opinion. Our mind knows he kicked the ball but there's no picture of him doing it. There's a picture just before he kicked it and a picture just after, so, when the frames are not in motion, your mind just goes fuck it and smokes a joint. So whither our noble VAR operators? They obviously have to pick a still image that either shows just before or just after and, as we've seen, the time interval is more than enough for a player to be onside in one and offside in the other. And also, what applies to pictures of the ball and foot also applies to the pictures of 'offside' players. In the end, what we see is a series of photographs that our mind connects together by filling in the missing information based on learned experience. The VAR operators are just picking photographs out of a lineup. IMHO. It would be nice if they showed two separate images with timestamps but that's just unrealistic because I doubt the equipment exists.
Using it for offside and claiming it's incontrovertible is bullshit. That's the problem I have with it. I don't like being bullshitted. Trust me I'm a(n) (ex-)referee/footballer. Yeah right. They are engaged in a futile endeavour but lack the wisdom to recognize the fact. Somebody has decided that's what they're going to do and they're all onboard like good little boys because their jobs depend on it. They should backtrack, stop what they're doing because they are making fools of themselves and use VAR for clear and obvious offside fuckups that nobody will argue about. They're getting carried away and self-interest comes into it no doubt. Organizations spend fortunes on tech when something cheaper would do and don't know how to use it. How often do they stop and say hang on we/I fucked up? Let's scale it back on offside.