Some of the forcefield shields are so big they can intercept shots, even those directed to adjacent units. All units on the same combat plane (either defense or fleet) as the source of such shield and within its radius will be protected from attacks. All shots directed to them will be taken by the protector shield, until all sources of protection have their shields depleted. After that, targeting will continue as usual, but later if a protector restores some shield, it will be able to intercept shots again.
Intercepted shots aren't connected to any target, so their damage isn't affected by unit specializations. Attacks that ignore forcefield shields cannot be intercepted.