Defensive Net

The defensive net is more a system than device. Relativistic bombardment works by two masses travelling at such speeds that both get eliminated in a super-energetic kinetic event. The key thing is to have your attacking mass as insignificant to you as possible, such as a single missile verses a ship. You can't go smaller than a steerable missile and keep a good chance of a hit as it is hard to hit a movable object without also manoeuvring.

The defensive net follows the same mass logic by surrounding the ship with small ball bearings held in place with clever magnetic field control. A relatively fast missile will hit a small ball bearing and both will plasmacise, where upon the missile will no longer pose a threat to the ship.

It is called a net rather than a shield as the ball bearings don’t touch.
The distance out from the ship, field depth, density and motion can be chosen by the Captain.
It is possible for objects to slip through the net.
During high energy impacts, mass and energy will still head towards the ship and impact. The difference is that on impact with the net, the plasmacising action causes pressure, which expands in all directions. In effect the net gets to redirect the energy.
The net can be mistaken for the hull and so missiles may detonate early, even at relatively low speed.