GURPS Basic Set covers the question of how high your skill levels should be with the Choosing Your Skill Levels box, on p. B172. Some other resources (GURPS Tactical Shooting, Guns Skill Levels, p. 42) also throw down what the right skill levels are for various archetypes.
Forget what skill levels mean. What can you do?
I’m assuming you will buy and use GURPS Martial Arts here.
Lets focus on a generic melee skill for a moment. Maybe it’s Axe/Mace, maybe it’s Broadsword.
Attack: This is default value for an untrained person. You suck. You suck so hard it takes a Telegraphic All-Out Attack (+8 to your skill, but +2 to defend against, and you can’t use your own defenses for the rest of your turn) to even get you to Skill-13. You may not use Deceptive Attack at all. Feinting is a waste of time for all concerned. If you thrust for the vitals, you will have a 50% chance of doing so, after which you will stand there with a “kill me” sign on your chest. If you try and hit someone in the head (-5) with that same berserker combo, you will succeed 25% of the time. Well, you’ll throw “a blow good enough to hit” that often; your foe will still defend.
Defense (Parry or Block): Bwa ha ha! Sorry, did you say parry? Your base defense on this one is 5 (3+Skill/2, drop fractions), and you’ll note most of that comes from the 3. If all your stats are 10 and you’ve no encumbrance, your Dodge is higher at 8, and at least with a retreat you can boost this to 11. You’ll be hiding behind a shield (for the Defense Bonus, DB), and probably choosing between All-Out Attack and All-Out Defense a lot.
Attack: This is what happens when Joe Average puts one point into the skill. You can do better than 50% chance to hit the torso with a Committed Attack, at least. The All-Out Telegraphic suicide attack at least gets you to Skill-17, which means you could hit the vitals 90% of the time with a thrust. At least you’re aiming for something important. You’ve got a 75% chance to bust someone in the face using that same move. You still are precluded from making real use of Deceptive Attack.
Defense: Still only a 7 for Parry (or Block using Shield, though you’ll pick up DB for many shields). Not great odds, but maybe with a retreat (+1) and a defensive attack (+1) carrying a medium shield (+2) you can eke out a 62% chance of defeating your foe’s attack. That’s at least better than 50-50, but not something to bet your own life on. You have very little margin against skilled foes.
Attack: Notionally the baseline for a professional, your raw hit chance is finally larger than 50%. You no longer need to stack several unattractive options to even have a chance of hitting your guy. You can do Committed Attack (Determined) and have a 90% chance of hitting his torso. You have a better than even chance with a Telegraphic Attack to the face (Skill-11), and you can finally look at the Brain as a viable target (AoA+Telegraphic for +8, Brain at -7, for Skill-11), or consider Committed Attack (Determined) to the vitals at Skill-11 and preserve your defense. You can target arms and legs (-2) at 50%, and this is the first fight-winning strategy that emerges without real penalties. You can hit arms and legs with a Committed (Determined) attack 75% of the time, even.
Defense: Your Block/Parry is now 9. Notionally, you now have the wherewithal to attempt a Riposte (and take -1 to your defense for -1 to your foe’s next defense), but I wouldn’t. While attacking cautiously as above, you will deflect 80% of blows (assumes a DB+2 shield). All-Out Defense for +2 precludes the Defensive Attack, but with the retreat and shield you’re at 90%.
You will still largely be choosing between “effective attack” and “effective defense,” but at least now effective means “pretty certain against lesser foes.”
Attack: OK. Now we’re talking. We’re not talking too loudly, since you still can’t hit someone in the face more than 50% of the time without resorting to Attack Options, but you can thrust to the vitals at 62% and give up nothing on the attack, or take a small penalty to defend (CA) and be at 83%. With an AoA(Determined) you can even go Deceptive, and inflict -2 to your foe’s defense and still hit 90% of the time. Better be sure he’ll go down with that blow, though.
Defense: Raw Parry and Block is now 50% (Parry/Block-10), and with the right set of options and Advantages, can start to get serious. Combat Reflexes, Enhanced Parry, Defensive Attack (+1) or All-Out Defense (conctrated) for +2, a DB +2 shield and a retreat (+1) and you’re adding a whopping 6-7 to this raw 10, giving you an “I’m doing nothing else but defending” total of 16-17. Effectively, at this point, lacking a skilled opponent or critical hit, you’re barely touchable if you go All Turtle, All The Time. At this point, especially if you have that shield and can give ground, you can Parry or Block over 80% of strikes and still have a viable offense. Your foes really have to ponder Deceptive Attacks of their own, or hope for criticals, because getting through your defenses is going to be a neat trick.
I’d call Skill-14 “entry level ass kickers.” You no longer suck.
Attack: Ah. Sweet victory. This is an utterly achievable skill level for entry-level DF characters. The Knight can get there pretty fast, and even well beyond given things like Weapon Bond and Balanced and choosing DX over ST, you can easily push a single skill to 22.
Still, at Skill-18, you can now hit the Brain better than 50% of the time, and use a Committed Deceptive Attack to the Vitals (!) to give -2 to your foes defenses and skewer him 83% of the time. Might want to only DA down to Skill-16, though, to preserve the extra chance for a critical hit. You can target arms and legs and either hope for the 10% chance to crit, or “only” accept a 90% chance at hitting and impart -1 to the foes defenses. Leg-chopping for fun and profit is viable here. More importantly, on really tough foes, you can target Chinks in Armor, dividing DR by 2, at 50% success rate . . . more with various Attack Options stacked up.
Defense: Base Parry/Block is 12, and you’re probably sportin’ Combat Reflexes too. You’re now looking at base Block/Parry with the +2 DB medium shield of 15 – now your foes have to start throwing Deceptive Attacks just to think about getting to you. And that’s without you really trying hard. With the right kit (such as a +3 DB shield) and Defensive Attack (+1), you can Riposte with a net defense of 14 and bequeath your foe -2 to defend against your own next attack, reserving your offensive bonuses for target location or soaking other penalties.
Attack: I bypassed Skill-22, which is totally cool, and the Dungeon Fantasy Knight, with the right kit and choices of stats, can start there. But I like Skill-24, because with it, you can take a -10 to hit for -5 to their defense and still rock their torso 90% of the time. But at this skill level, you should be thinking (a lot) about chinks in armor (-8), the brain (-7), and really think about crippling arms and legs, or hands and feet. You can to this and still hit them with up to -4 penalties to defend. You have so many choices here that you may not need to make them, and your defenses will be so high that accepting the defensive penalties from Committed Attack is par for the course.
Defend: Your base Parry/Block is a mighty 15. Toss in Combat Reflexes and a DB+2 shield and you’re at Parry/Block of 18. Back up and you’re at 19, Defensive Attack and you’re at 20. Yow. You’re going to be Riposting. A lot. Why wouldn’t you? Sure, against tough foes with Skill-18 throwing -2 or -3 Deceptive Attack penalties at you, you’re down to a measly 12 or 13, but right back up there with a little cautious fighting.
So, there we go. Clever GMs will find ways to make high skill not matter (such as high DR, or if the PC is silly and combines all that skill with ST 8 or something) in all circumstances. For “real” fighters, you’ll want to be in the Skill-14 to Skill-18 range, which gives a nice sliding scale of offense and defense. For real badasses, you’re going to want to be Skill-20 or higher. I just loves me the -10 Deceptive Attack for -5 to defend, though.
Also note that in grappling, many techniques make use of Contests of Skills, rather than attack/defense rolls. I have never really sat down and worked through the math of that the way I have with attack/defense. Perhaps that will be a subject for a future post. I bet the results are different in important ways.
Edit: A very, very late add, but over at Renovating the Temple, +Patrick Halter has published a nice analysis of how much Deceptive Attack you should take given attacker and defender’s skill. While there are some edge cases, being deceptive down to the 14-16 range is rarely stupid, if occasionally not precisely optimal. It’s nice work, with a fairly easily understood graphical presentation. Nice work.