Right now, grabbing sucks. There's a reason you only grab someone who's stunned, handcuffed, or knocked out/dead. Why? Because they can immediately move a tile or two away and get out of your grab.
So here's my proposal: grabbing someone stops them from moving, either until you let go or they resist (like resisting out of handcuffs, you know?) their way out of it. The higher the level of grabbing (passive > aggressive > the neck), the harder it is to resist your way out.