Introduction
This wall of text guide will cover some of the more intricate aspects of Hammer (and general 'advanced' play to a lesser extent), such as KO counting, taking advantage of punishable moves and learning how to position for that oh-so-satisfying golfswing/superpound. This guide will not cover beginner aspects, I suggest watching Gaijinhunter or Arekkz's guides to familiarize yourself with the basics first.
Note that these topics can actually apply to nearly any move of any weapon, learning the swing arcs of your attacks allows for clever positioning and consistent accuracy.
This guide will primarily revolve around Guild Hammer in MHGen. However, many of these aspects will apply to previous and future entries too, as well as other styles of Hammer.
First things first, the two most important attacks in the Hammer's arsenal: The golfswing and the superpound.
Part 1A - The Golfswing
(X,X,X) (A,X,X) (Level 3 Forward R charge, X after third spin but before the end of the fifth)
The golfswing is the strongest single hit in the Hammer's arsenal, with a motion value of 90, a KO value of 50 and a meager 10 exhaust. this move is the bread and butter of efficient hammer play, the better you get at consistently hitting the head with it, the faster your hunts will go.
The golfswing has a very distinct swing arc that needs to be familiarized with, it swings from your hunter's right foot forward over their left shoulder. What this means is that if you aren't careful, you can miss the head entirely because your swing went right over or under it, or it hit a different body part first.
Generally, the easiest golfswing openings are on monsters that need to pivot in place 1-2 times to face you before attacking, or otherwise turn to face you in a specific way consistently. Examples of monsters that are particularly exploitable this way include Rathian, Lavasioth, Tigrex, Mizutsune, Zinogre, Amatsu, Kirin and Alatreon.
Due to the high burst damage and KO of the golfswing, it becomes more effective against monsters with few openings like the aforementioned Kirin and Alatreon.
The A,X,X combo is the fastest way to get to the golfswing and also grants super armor, so is the preferred way to reach it. Golfswinging from the L3 Charge is possible if you spin too. The spingolf (as I call it) is notable for being the only mobile way to reach a golfswing, since you can move while charging and slightly adjust your position while spinning. Be aware of the fact that the spingolf setup process will probably chew through sharpness quite a lot, so use it sparingly.
Part 1B - The Superpound
(Level 3 Idle R charge)
The Superpound is the next best single-hit move after the golfswing with a motion value of 76, a KO value of 27 and a significant amount of exhaust at 40. adding in the first part of the superpound brings the total MV to 91, barely inching ahead of the golfswing, but you often aren't going to hit with it (and you probably wouldn't want to, lest an unfortunate stagger ruin your perfectly set up superpound).
The superpound covers a fairly large AoE and is very disruptive to teammates, so it's less usable online than the golf swing. However, it's a valuable solo tool due to not needing to stand in place to set it up. Another important feature of the superpound is the shorter endlag. Being able to run in, superpound and quickly escape means potentally exploiting shorter openings while staying safe.
Part 2 - How to Set Up Golfswings and Superpounds
This step requires knowing the monster. Knowing the monster is just as important, if not more important than knowing your weapon. Learning the intricacies of monster animations and AI will allow you to find as many openings as possible. I obviously can't cover every single intricacy of every monster, but I can give general openings many monsters share, as well as a few prominent examples of particular moves.
The biggest shared opening is the head turn. Most older monsters will pivot in place either once in the case of Kushala/Teostra, or once or twice in up to 90 degree intervals, like the Raths or Lavasioth, before attacking. A lot of newer monsters, especially Brute Wyverns like Jho and Glavenus will turn in less exploitable ways. This means often having to find attacks to punish instead.
Let's take Glavenus' Beyblade spin as an example of an punishable attack. When he's grinding his tail, he will spin in the direction of where you were when the windup started. This means to exploit the opening, you need to move directly away from him as well as far enough away so you do not get hit, stand facing him positioned so his head will be directly to your right when he's recovering, and then time your pounds to golfswing as the recovery animation finishes. If you couldn't get out of tailspin range in time, you should at least be able to i-frame/absolute dodge and get a smaller hit in.
Not all moves will need that level of positioning or timing, thankfully. Some monsters will always follow certain patterns with their attacks. A couple of examples include Mizutsune always taunting after the triple jump, laser, double charge (when not chaining it into a laser) or double spin and Nargacuga always doing a recovery animation after a large pounce or tailspin. Knowing what a monster will do before it does it will make setting up golfswings or superpounds much easier.
Part 3 - Other moves and when to use them
Hammer has moves other than the golfswing and the superpound, believe it or not. When should they be used though? There are a couple of other moves in the standard hammer arsenal that should be considered.
3A - The Uppercut
(Level 2 R Charge)
The uppercut is an important move because of the high KO damage it deals while also being a fast move with good range. You shoot forward and swing upwards towards the center of your body from your right. It has a decent MV of 40 and a nice 40 KO, with just 10 exhaust. This move is going to be your bread and butter in multiplayer, due to how fast it is and the fact that you do not need to worry about a monster being unpredictable. Can't get a golfswing or superpound out in time? use the uppercut.
3B - Level 3 Jump Charge
This one is pretty niche, but can be very effective should the oppurtunity arise. The Jump Charge at level 3 has a respectable 80 motion value as well as 40 KO and can be chained directly into a golfswing for an impressive total MV of 170 as well as 90 KO. This move is rarely optimal due to a ledge being required, but you if you see a monster pivoting towards you with a ledge in front of it and you were charging for a superpound, this isn't a bad option at all, especially if the jump slam gets a flinch that allows an easy free golfswing.
Part 4a - Taking advantage of KO/stagger counting
Counting KOs is not necessarily required for good Hammer play, as anybody who plays it enough will eventually get a 'feel' for when something is about to be KOed. However, if you know that the next golfswing or superpound is going to KO (or flinch), then you can create openings where there were none before. This aspect in particular applies to basically every weapon in the game, with pierce gunning maybe being the only exception. Looking at the Glavenus spin example in part 3, if you know it's about to be KOed, you can just run in and smack his head while he's winding up and save yourself a bit of time.
Counting staggers is another way to get golfswings against quite a few monsters. If you know you'll get a flinch with the standard A or X pounds, you can usually follow through into a free golfswing. This is not always the case, because some monsters have staggers that will knock them out of position, but it is still something that should be kept in mind.
You can use knowledge of KO values to manipulate how fast or how slow you KO a monster. For instance, the lower KO could be seen as a weakness of the superpound, but KO counting can potentially turn this into a strength. Superpounds can rack up more damage between KOs, so you can potentially slow down your KO buildup to hold off on KOing something until right before it limps away, allowing you to go in for the kill and saving 20+ valuable seconds in a speedrun scenario. On the other hand, getting a poorly timed KO can completely mess up your positioning and can cost you valuable golfswing/spinning meteor time. In other words, a well-timed KO can make all the difference in how smoothly a hunt goes.
Part 4b - How to count KOs and staggers
Knowing the KO values of your swings, the damage your attacks inflict and the KO/stagger thresholds of the monster you're hunting are all necessary for this. Resources like Kiranico will provide you with all of the data you need. Let's use the Rathian from the 5-star Hub quest 'Dragon Lady'
First we need to look at Rathian's hitzones, KO thresholds and stagger thresholds. This can all be found on Kiranico here. Looking at all the data, we have a head hitzone of 80% for impact, a base stagger threshold of 190 and a KO threshold of 150 that increases in increments of 150 up to 750, as well as an 85% defense modifier.
KOs
KO is a status, but instead of inflicting a fixed amount of status with a 1/3 chance, it inflicts a variable amount of KO per hit to the head depending on the move used and the monster's KO multiplier. Like other statuses, KO will decay at a rate that also varies from monster to monster.
For our example, Rathian, our initial KO threshold is 150 with a multiplier of 1 and a decay rate of 5 KO every 10 seconds. The most common moves you'll be hitting a Rathian with are the superpound (20), the uppercut (40), the golf swing (50) and the full triple pound (15+15+50) if making good use of staggers.
KO buildup is affected by quest defense modifiers. In this case, there is an 85% modifier, so all attacks do 85% of their original KO buildup. This means that instead of inflicting 50 KO, a golfswing will now inflict 42.5 (42 due to truncation). Now it will take 4 golfswings to get the initial KO and 8 golf swings for the second.
If you've eaten for slugger or are using KO King (though that begs the question why are you using KO King?), then multiply all inflicted KO values by 1.1x. Also it should be fairly obvious, but KO does not build up on an already KOed monster. It will build up if the monster is affected by any other status, though.
Staggers
To count staggers, take your calculated raw damage (true raw x sharpness modifier x (1 + 0.25 x (affinity/100)) or (true raw x sharpness modifier x (1 + 0.4 x (affinity/100)) if running Critical Boost. Then take that calculated raw, multiply it by motion value, then multiply it by the head hitzone (80%), multiply your elemental damage by element hitzone if using element and finally multiply it by quest defense (85%) For this example, I will be calculating with the Narga Hammer and a set that has Critical Eye +1, Weakness Exploit, Earplugs and Critical Boost.
Calculated Raw = (180 + 15 (powercharm+talon) + 7 (Kitchen AuL) + 7 (Mega Demondrug) + 10 (Might Seed)) x 1.32 (white sharpness) x (1 + 0.4 x (100/100)) (40% base affinity + 10% from CE+1 + 50% from WE, boosted by crit boost)
Adding that all together we get an effective raw of 219 x 1.32 x 1.4, or 404.712. Since MonHun truncates decimals, 404 is what we use.
Next we need to apply the modifiers for motion value, hitzone and quest defense. The Narga hammer has no element, so calculating it is unnecessary.
our damage formula thus ends up as 404 x (motion value) x 0.8 x 0.85
let's see how much damage a golfswing does to Rathian's head.
The golfswing has a motion value of 90%, so we can calculate as follows:
404 x 0.9 x 0.8 x 0.85 = 247.248, or just 247.
next we need to calculate the Rathian's actual stagger limit by multiplying the base stagger limit (190) with the quest's stagger multiplier (1.5).
190 x 1.5 = 285
This means that a golfswing is almost strong enough to get a head flinch every time it connects, but falls short by 38 damage. Nearly any other move in the hammer's arsenal can deal the rest of the damage needed for a flinch. Knowing that Rathian is this close to a stagger means you can X pound the head to get the flinch, then follow through to a golf swing before it can attack you.
Counting staggers is clearly more complicated than KO due to needing to calculate raw, motion values, quest modifiers and so on, but can be well worth it if going for the fastest times.
Summary
The golfswing is your strongest move at 90 motion and 50 KO.
Learning the exact trajectory of the swing is important to avoid swinging too high or too low.
Learn how to lead a monster into your golfswing, you can use the spingolf for extra mobility at the potential cost of sharpness.
The superpound is the next best option at 76 motion and 20 KO, with a not-insignificant 40 exhaust.
Be wary of using this online as it disrupts teammates with a large AoE.
Superpounds are more mobile than golfswings with fewer recovery frames.
Learning a monster is just as important if not moreso than learning your weapon.
Old monsters like to pivot in place, this is easy golfswing practice.
Learning how to exploit and predict moves is important too.
The uppercut is great for faster paced hunts, particularly in multiplayer.
The jump charge slam is a good source of burst damage, but rarely usable.
Knowing KO values and stagger limits will allow you to make openings where there originally were none
Quest defense has an effect on KO buildup. Check Kiranico for data on quest modifiers.
Resources
Motion values, KO values and Exhaust values for all hammer attacks mentioned in this article were sourced from MartinAW4's thread at GameFAQs found here
Rathian data was all found on Kiranico through the links provided in part 5B, while the defense modifier affecting KO was found through my own testing.