Here's how I understand the options for defense rolls, based on FAQ and BBB:

1. Reaction (ranged defense)
2. Reaction + Dodge (melee defense *or* ranged full dodge)
3. Reaction + Weapon Skill (melee parry/block)
4. Reaction + Dodge + Dodge (melee full dodge)
5. Reaction + Weapon Skill + Dodge (full dodge w/ parry)
6. Reaction + Weapon Skill + Weapon Skill (full parry)
7. Reaction + Gymnastics (Gym. Dodge vs. Ranged)
8. Reaction + Gym. + Dodge (Gym. Dodge vs. Melee)
9. Reaction + Gym. + Weapon Skill (Gym parry?)

Am I correct?

Yes. Although note that since these skill values don't go up and down there will normally only be three values:

1. Ranged Defense
2. Melee Defense
3. The Full Defense Bonus

In most cases street samurai get a very large Gymnastics (because it's so easy to pump with Synthacardium), and then the full defense choice is always Gymnastic Dodge.

Magicians and hackers often don't bother with getting close combat skills or pumping athletics, so they'll get a Dodge skill.

-Frank

Actually, I've yet to see a player who was aware of the gymnastics dodge even bothering to take the Dodge skill.

To balance this out a bit, I've interpreted #8 to be wrong: You can't add a Dodge skill to your melee full defense. The double dodge bonus is reserved for the dodge skill.

Yeah, I tend to NERF Gymnastic Dodge because otherwise taking the Dodge Skill is a foolish move.

Well that plus I've always hated it when my players try to describe their fight scenes like something out of a bad Japanese Fighting/Dancing Movie.

I wouldn't use gymnastics dodge for every sammie or combat adept, but it is a viable option. You can pump it up so many ways - synthcardium, enhanced articulation, reflex recorders, and adept improved ability (at only 0.25/level, compared to 0.5/level for dodge). But it is only really decent for full defense against ranged combat. For characters lacking a good melee skill to counterattack with, dodge is the better choice. So it usually breaks down like Frank said.

What are the specific rules for Gymnastics dodge?

The way we play it now you can only use Gymnastics as your dodge if you are doing something that would allow gymnastics to be a plausible recourse. Example: If you are running from combat on a long straightaway, say down the road, it is fine to use Gymnastics dodge with the assumption that you can perform cartwheels or something similar like you would see in a bad sim. Or if you are currently performing some sort of gymnastic feat, like climbing something similar to monkey bars.

If we are in a firefight in an office hallway we can't use gymnastic dodge because the idea is just absurd. I might let it slide with a phys adept with wall running, but otherwise it just seems silly.

I just ignore the dodge skill.

I treat gymnastic dodges as someone just being co-ordinated so good at moving quickly and unpredictably in a controlled manner to make themselves harder to hit.

I can't see why dodge is a separate skill.

Thanks for the replies. Specific question: I had a scenario where a sam took a couple rounds and decided to go on full defense and try and make a jump into some cover (he was standing in front of some oil drums). Is that gymnastics or jump?

That's up for debate. Since Gymnastics is listed as an atheltic skill, using it to dodge can be considered an athletic test. You'll note that I didn't say those dice applied to the dodge roll, although that is a strong implication.

Basically, there's not enough evidence either way to say one way or the other. Personally, I'd let it; based on the RAW, you may as well dump the Dodge skill in its entirety, it's just useless compared to gymnastics anyways. This makes it easier for people to pump their dodge dice.

Oh and don't forget the modifiers. Most common being +2 from running which is applied as a bonus to the defenders defense roll as opposed to a penalty for the attacker.

Personally I don't like that as it doesn't matter if you're running if you're surprised as a result of not getting a defence roll, but there it is.

Here is a link to the FAQ

http://www.shadowrunrpg.com/resources/faq.shtml

Which says:

What exactly is the dice pool used in the Full Defense option Gymnastic Dodge (p. 151, SR4)?

Against ranged attacks, it would be Reaction + Gymnastics. Against melee attacks, it would be Reaction + Dodge + Gymnastics or Reaction + melee skill + Gymnastics.