Stealth in structured encounters is in serious need of some TLD (tender-loving development). The best right now is Ambush, which adds damage, but that's about it. A guideline for a structured stealth encounter would be really nice.

I think you can handle it with the tools we're given, no need to make up new rules.

First it has to be appropriate for the in-game situation. You can't just hide in combat if there's nothing to hide in right?

So, say you're in a dense jungle, in combat. PC and NPC are already aware of each other. Okay, PC goes Stealth, probably has to spend a Maneuver as you aren't just cloaking - you're moving into a hiding place as NPC is already aware. So they make their opposed test and PC wins. Ok that's PCs round, right?

The NPC could probably attack them with 100% cover penalties, swinging/shooting wildly in the area of where they were last known to be. As GM I'd say there could even be a further Setback for the successful Stealth, there is cover but they also moved right? And/or NPC could also make another Skill check to find them. Would probably give them a Boost as the area the PC could be in is limited. Other Boosts for other appropriate gear (scanner goggles, etc.).

Next round, PC would probably Follow the ambush rules and could of course aim or do whatever as usual.

If you're not in a situation where there is cover - including darkness - all around, you're really just in cover, I think.

You could give the 'hider' a Boost(s) and the hidees Setback(s). In all honesty the 'hiding' in the middle of a fight where you were seen and now you aren't thing is a little silly.

I think they purposely didn't include hard and fast rules for stealth because it is so dependant on the situation, but the dice tend to be flexible enough that it works.

I'd say, when not yet being detected, a stealth roll will keep you hidden unless you do something that will obviously reveal you (like attacking in most cases, unless you are far enough away to not draw attention with a ranged weapon, use silenced weapons, etc.) or the circumstances change, which would call for another stealth roll.

If an enemy has already noticed you, you should only be allowed to try to roll stealth if there is a logical environmental factor that allows you to lose your enemy. You can't hide behind a crate in an otherwise empty room, but when being in dense underbrush, or when a bigger object allows you to lose line of sight so you can subsequently move to a hiding place unseen, I'd say go for it. As for mechanical benefits, they can range from the enemy simply unable to attack you because they've lost sight (this is GM discretion though, sometimes an NPC could be smart enough to know where one would hide), needing to spend maneuvers to get into a position where they could theoretically see you, performing a perception check to find you, granting the hidden character defense, etc., and that all can be used in conjunction with the dice results.

Attacking out of stealth can be done with talents (Ambush as mentioned before), and don't forget that the enemy is already wasting his round to come looking for you, so that's quite an advantage I'd say.

Well, stealth in combat should have at least 1 setback if there are enemis watching the character trying to do this, and another if there is no places to hide.

But it's possible to try some distraction as well.

I guess the character who succeed could use advantages to have a bonus in the next skill check or something like this, but it's hard to know, cause there are a lot of possibilites. It's how the system works.

The character could do it but he found a poor place to hide during the combat (behind the enemy lines) or found new enemies trying an ambush, idk.

A lot of this depends on the situation.

First he needs a place to hide. If there isn’t an apparent place to hide I would allow a story point to create a hiding place.

Second, he would either need to be unobserved when he hid or the hiding place would need to be big enough to not allow the enemy to pinpoint his location. The the former this is difficult in combat, but for a stealth roll with triumph I would allow the enemies to be distracted and not see him hide. For the latter, if the area is big enough (e.g. an area of darkness) then I would say the enemy can not pinpoint the location without a successful perception check, and then they would get a couple setbacks to make the attack.

If the character is attacking while hidden then I would allow a couple boost dice for the attack.

I blame World of Warcraft, and Star Wars: The Old Republic, for the issues here.

Personally I would say the RAW provide you with mechanisms to support this, and you need to break players away from the CRPG idea of being "in stealth" - a ridiculous form of invisibility - to being viewed as non-threatening or, if in a crowd, not a target.

Examples:

The SWRPG talent "indistinguishable", if used in Genesys (and am away from book, so can't verify), coupled with a good stealth check, could help you blend in. Otherwise, holding back from a group so that you could conceivably duck behind a pillar etc and avoid being seen makes sense. Then for "backstab" - we don't really do damage modifiers like d20 does, but that's ok because the player has used the environment to get a shot off on an opponent where the opponent was unready for it. And, genesys allows for environmental boosts via boost dice. The way in which the scene plays out would determine how many are added. If it's a warehouse fight with limited lighting and lots of crates and racking to move through unseen? 2 boost. If it's a wide open room, then maybe a successful deception check to appear to be a non-combatant, before getting the attack off.

But also, I have someone going for a rogue-like build in my fantasy Genesys, and I've said "don't think daggers and backstab", because the ridiculous limits of d20 need not apply. Once you get that good surprise hit in, you'll be in the thick of the fight so make it count, but also, carry a sword. Or something more than a knife.

It just occurred to me a cosh being used in this way could be a great thematic play for a roguelike to try and disable a combatant from a fight, to interrogate later...