I got this random scenario in my head recently, which I wanted to test myself but can't currently. Suppose you get pinned by an enemy Reinhardt and then, while Reinhardt is charging away with you, you get hooked by an enemy Roadhog. What happens? Does the hook get broken? Does it not connect at all? What happens if it attaches to the victim? Do they get pulled out of the pin?
I'm pretty sure the hook would grab you while you're getting pinned, but it's important that the rein doesn't keep charging to an area where roadhog's hook it stopped during the animation. As long as you're in the area where the roadhog could hit you and it doesn't get cancelled, you would most likely be pulled out of the charge.