In terms of losing a cloaking device, do I have to be allowed to roll defense dice for damage assigned to be a hit?

I'm asking because I don't think hitting an asteroid counts as a hit but am curious about other instances.

If a dice was rolled and you didn't cancel the boom or kaboom result with an evade you have been hit.

However damage from cards like ruthlessness do not knock off your stealth device, although you took damage you were not hit.

There are two ways to be "hit" in X-Wing:

1. Rolling less evades than the attacker rolled hits or critical hits.

2. Being attacked by Lt. Blount (Rebel Zed pilot).

I assume you meant Stealth Device, it is only removed when Hit by an Attack, any other source of damage (bombs, obstacles, Feedback Array, Ruthlessness, etc.) won't affect it.

Hit is a term that is defined in the Rules Reference.

I assume you meant Stealth Device, it is only removed when Hit by an Attack, any other source of damage (bombs, obstacles, Feedback Array, Ruthlessness, etc.) won't affect it.

Yes I meant a Stealth Device.

Hit is a term that is defined in the Rules Reference.

RRG, pg 12:

"HIT

During the “Compare Results” step of attack, a ship

is hit if there are any [HIT] or [CRIT] results remaining

after canceling dice.

So this means taking a hit or crit from an Asteroid counts as a hit?

Hit is a term that is defined in the Rules Reference.

RRG, pg 12:

"HIT

During the “Compare Results” step of attack, a ship

is hit if there are any [HIT] or [CRIT] results remaining

after canceling dice.

So this means taking a hit or crit from an Asteroid counts as a hit?

No, the Asteroid isn't an attack, and doesn't have a "Compare Results" step.

There are two ways to be "hit" in X-Wing:

1. Rolling less evades than the attacker rolled hits or critical hits.

2. Being attacked by Lt. Blount (Rebel Zed pilot).

Amendment to number 1: after canceling dice during Compare Results, there are one or more [boom]/[kaboom] results that remain uncanceled. (Covers things like Autoblaster, Ten Numb.)

In terms of losing a cloaking device, do I have to be allowed to roll defense dice for damage assigned to be a hit?

I'm asking because I don't think hitting an asteroid counts as a hit but am curious about other instances.

You mean Stealth Device but in most ways you are correct.

The only way to be "hit" by an attack is to actually be attacked. Being attacked means going through that big long process which would include rolling defense (even if you don't actually have any dice to roll) and comparing results. You are "hit" if there are uncancelled [boom] or [kaboom] dice after that step. The one exception to this is Lt. Blount whose attack always "hits" even if the dice say otherwise; this means his attack may not do any damage but will still trigger anything that happens on a hit.

If something just causes you damage that does not count as a "hit" in game terms. I guess a crazy example of this could be Wampa who attacks you and then before the compare results step cancels all hit attack dice to deal a damage card to the target; here the attack actually misses (no attack dice means the defense always wins!) but damage is suffered as demonstrated by being dealt a card.