Trying to find out what these force fields are canonically supposed to be, I stumbled upon the fact that the place where this fight scene occurs is the Theed Generator Complex - the main power generation facility for the capital city of Naboo. And they built it right next door to the royal palace.

I guess you don't want the Queen to wake up late because her alarm clock lost power in the middle of the night. Or to be, you know, safe from any sort of industrial accident that might occur at a huge power station.

Transcript

Black-Robed Figure: Can I get a word—
[SFX]: 18!!
[SFX]: Whooom!
[SFX]: Krzrzrkkk!
[SFX]: 6!!!
GM: Oh for crying out—
{force fields appear, separating the combatants}
Black-Robed Figure: Right, now I can finally talk.
Obi-Wan: Force fields? What on earth are these here for?
GM: Airlock.
Obi-Wan: Why are there so many of them?
GM: Um... it's a redundant system.
Obi-Wan: But we're in an atmosphere.
GM: ... They do vacuum testing of fighters in the hangar.
Obi-Wan: The hangar with the huge open-air entrance?
GM: It also has a force field.
Obi-Wan: I wonder why the Trade Federation didn't raise it to trap our fighters.
GM: It... blocks air but lets metal through.
Qui-Gon: I disguise myself as a robot and walk through! 17 for Bluff!
GM: No.