See, and I went the direction of “grabbers grab+pull, all zombies grab+slow” because it made grabbers dangerous for once and the “pull” action less frequent because if every zombie does it, then I felt it might get tedious.
It makes windows still “safe” when there are no grabbers around, but if there is one in the pack you need to fall back and plan-B it.
However, I do sympathise with inadequate's point that attacks which involuntarily move the player can be frustrating (similarly to paralysis) so I'd suggest that all zombies have a chance of slowing you down occasionally (as Kevin says 'just getting close and getting an attack in occasionally would be good enough.') if they get close to you, with a (very) small chance of dragging you backwards from the direction you came. I'm not sure how to code this, but I'll have a look.
There is always the “tired” condition. Up the chance of getting pulled around if you’re “tired” or worse. It’d signify the lack of ability to fight back due to exhaustion. It’d make being tired (and worse) something to actually consider taking care of instead of just waiting until you get to max sleepiness then going to bed for a day.
I think zombies already have a chance of pushing you out of the way of a window which could be raised if it's already in (if not, it should be), as I think getting rid of the terrain exploitation should definitely be cut down for any sort of classic mode, where you don't have special zombies that can counter such tactics.
I’ve never had it happen from normal Z’s. Only time I’ve been moved was specials (at least I think I moved), and it was because the whole wall exploded when it rammed through.