I found an item with the following attribute:
Chance to tether yourself to an enemy.
When I get shooting at people, sometimes I can see this in action. I see a green beam form between myself and the enemy. As far as I can work out though, that's the extent of this feature. It doesn't appear to restrict movement of either party, and if I move far enough away or kill the tethered enemy, it disappears.
Does it do anything useful?