Well I think it could be made perfectly believable. How about this? (This is the map briefing) The cargo freightor is smuggling desperatley needed arms and supplies off to a rebel world (or off to meet a rebel ship for the handoff). Its coming out of a backwater world with only a lightly armed Indictor ship with gravity well generators out there to inspect the cargo (something I'd expect would be routine in a controled society such as the Empire). The imperial captian orders the cargo ship's captian to open the hangar bay, and remove all crew members from the cargo and hangar area at once, for security reasons. Alright the map starts here.
The imperials can spawn in their hangar, and take their transports into the cargo freightor, then walk into the cargo bay for the inspection. There aren't any rebel spawn points in this area of the ship where the imps are, so their isn't any contact between the two groups yet. Once an imperial enters the cargo hold it sets off a trigger (just like the trigger in the titan in 2142, when an enemy enters and the loud speaker warns u). The trigger sets off a verbal warning over the ship's intercomm by the Imperial captian, saying that illegal ordinance was found in the cargo hold, and demanding all crew members to surrender peacefully and announcing that gravity well generators are preventing the ship from fleeing. The same trigger also opens several doors in the inards of the ship (allowing the imps to push deeper in), as well as opening several new rebel spawn points in the rafters of the cargo hold (where rebel forces where hiding waiting to ambush the imps below if things went sour). So the battle begins in earnest.
Theres a secondary hidden cargo hold deeper in the ship, with a hidden door that opens to out side space. A hidden hangar bay basically. This is a reb spawn point. In several opened crates there are a few xwings, that can fly out. The rebs need to use these to disable the Imps gravity well generators, allowing the freightor to hyperspace away. All while holding the imperials at bay in the ship's innards. The imperial infantry need to either destroy the hyperdrive in the engine room, or capture and hold the bridge to win.
The imperial indictor dosn't have the fire power to pierce the cargo ship's heavy shielding, and the captian refuses to fire while his own troops are aboard anyway.

Futurama: You Can't Prove it Won't Happen

Well the justification here, as I said above, was that the Captian was refusing to destroy the ship while his troops where on it. And they where there for a completely normal cargo check, before any hostilities began (seeing as the rebs where hoping that the illegal goods wouldn't be discovered). So before he even considers destroying the ship, he already has troops on it. And if you've already got troops on a vessel, have the ability to prevent the vessel from escaping (grav well generators), as well as the ability to put more troops on it, why would you destroy it? At the worst he could keep it there until reinforcements show up.
And then once the rebel fighters launch, the imperial transports would be too vunerable to try to pull his troops off. And he obviously dosn't want to destroy a ship his troops are on.

Futurama: You Can't Prove it Won't Happen

Ya, I'll go with that ^

Futurama: You Can't Prove it Won't Happen