Is there something about the slam rules I'm missing?
 

A female cheetah uses a pounce (B372) against a partially surprised male impala, as the description of pounce suggests. ("This is how some animals attack, especially cats: they knock down their foe and then claw or bite.") The cheetah is running at speed 24. The cheetah easily makes her attack roll and the impala fails to dodge. They "each inflict dice of crushing damage on the other" (B371). The impala takes 2d crushing damage (2.16, round down) and the cheetah takes 3d. (2.64, round up as per B371.)

On average, the impala takes 6 damage and the cheetah takes 9.5 (because both have DR 1). The impala takes less damage, so remains standing, unless he takes a major wound and fails his knockdown roll. The cheetah is more likely to have a major wound, as likely as not to be at 0 HP or lower, and must make a DX roll or fall over because of the special rules on flying tackle. (If the impala rolls twice as high as the cheetah it's possible the cheetah's down anyway, depending on your interpretation of "On a success, you stay on your feet!" under pounce on B372)

It seems like unless you can manage to arrange your velocity such that your damage is above a rounding breakpoint and your opponent's is not (hard to know unless you exactly know your foes HP) then a slam of any kind is a really bad idea, unless you have armor (which limits your velocity) or a shield or spear to absorb the damage. Even if you can manage to arrange the damage around a breakpoint, if you're an unarmored martial artist, you're risking a major wound even at 1d, and therefore at risk of getting stunned or knocked over.

Is there something I'm missing here?

Re: Is there something about the slam rules I'm missing?
 

Huh. This is interesting. But I think the cheetah would do a basic 3d-3 damage - I interpret the fractional rules as applying to partial dice damage in a slam, i.e. 2.16 dice is 3d-3 - plus a Brawling bonus of +1 per die and also an All-Out Attack bonus of +1 per die (see Martial Arts 98). So I would say that the cheetah would do 3d+3 damage and the impala 3d.

(Incidentally, I notice that Pizard's cheetah template is missing Sharp Claws, for some reason. Also, I suspect you can find video footage of cheetahs getting pretty messed up by adult male impalas.)

But even though it says this is a common tactic for big cats, I don't think a cheetah would Slam an adult male impala. I think a cheetah would do a Move and Attack to grapple, then bite (with Sharp Teeth), then worry, and I think it would probably choose a smaller impala, if possible, not an adult male. I suspect the pounce is more commonly used by other big cats, whereas cheetahs use their speed to make a regular Move and Attack.

But no, I don't think you're really missing anything. Slams are dangerous for the attacker!

Edit: Took me a little while to find, but this thread might be interesting. Especially the Tackle technique at the top: https://forums.sjgames.com/showthread.php?p=2422249.

Also, the DFRPG version of Slam is a bit less problematic, and I think a lot of folks use those Slam rules instead of the rules in Basic.

Re: Is there something about the slam rules I'm missing?
 

Yep. A Slam isn't the right attack here. It's not just a brutal collision hoping to knock down and/or overrun the target without concern for the attacker being injured. It's a skilful move that has the claws and paws striking and grappling rather than the body just impacting.

Re: Is there something about the slam rules I'm missing?
 

I made some martial styles with a few custom techniques for animals in my Animal Combat article.
But that kind of attack can be handled multiple ways. I dont really consider it a slam so much as the poster above suggested a Move and Attack.
Other factors. The prey is likely running away, reducing damage from velocity rather than increasing it if both ran at each other.
The animal can also use up velocity/momentum by leaping and then falling instead of a full speed direct impact.
I should have added such a note to that article!
Here is a sample technique from that article, it has a few new techniques plus a style for various types of tactics. Ambush Predators; Rushing or Stalking Predators; Pack Predators; and Prey Animals for example.
Deadly Pounce
Defaults: Brawling, Jumping, or Wrestling.
Prerequisites: Brawling, Jumping, and Wrestling and
requires four legs; can’t exceed prerequisite skill+2.

This is an All-Out Attack (Double) that combines a Pounce
(p. B372) followed by a grapple attempt. It allows up to a half
move forward with an extra yard of reach and +4 to hit for a
slam, followed by a bite to grapple. Roll DX, Acrobatics, or
Jumping to stay on your feet afterward.

Re: Is there something about the slam rules I'm missing?
 

I'd houserule that too, but the rules on B371 make it pretty clear that RAW you're supposed to round unless you would round down to 0, in which case they've got special cutoffs for partial dice.
B182 makes it clear that brawling gives a bonus to your thrust damage when making brawling attacks. Slam is a brawling attack (in that it is an attack roll based on brawling) but its damage is unrelated to thrust damage and has its own calculation method. Thus, the bonus damage from brawling would not apply. I've heard there's an updated ruling in Martial Arts that allows you to add the brawling damage bonus to slams anyway, but I've not been able to find it.
This is, I'm finding, a pretty common thread between replies. It seems as though pounce is mechanically ill-suited to its intended purpose.
Thanks! I'll 100% check those out!
This seems mechanically weird to me. If I'm interpreting the rules right, you'd be making this second attack at a penalty due to shock, which would make it hard to land the grapple. If you limit your velocity such that the pounce only deals 1d6 damage or less you can mitigate that, but it still begs the question of why are you're making a pounce attack in the first place.

All in all, I feel like the pounce as implemented in Basic is better suited to be used by high-HP quadrupedal warbots that have enough DR to avoid damage, and to be used against unarmored targets that don't. I just wanted to make sure there wasn't anything I was overlooking before coming to the conclusion that large cats shouldn't pounce.

Re: Is there something about the slam rules I'm missing?
 

I think I figured out how to make this Cheeta-pounces-Impala thing work folks.

1) Cheetah launches a 3-attack Combination

2) step 1/3 is to grapple something you can lift off the ground - a cheetah can't lift the ENTIRE impala off the ground, but it CAN lift it's LEG

3) step 2/3 is a "pickup" technique (Technical Grappling) w/ some modification when you're just lifting up a leg instead of an entire creature (we need rules for that)

4) oh look, when I am grappling a person I can lift off the ground, I can use them as a shield to block with (B375) so surely if I can lift the LEG off the ground I can block with just the LEG

5) but wait, if I have an improvised Shield, then my Slam can be considered a Shield Rush

6) in the case of a Shield Rush the HP you would normally suffer from hitting your target is instead suffered by your shield

7) step 3/3 of the combination is the "pouncing shield rush"

In conclusion: the cheetah grabs the leg of the implala and shield-rushes that leg into the imapala's torso (or maybe it's other leg) and the pounce does not harm the cheetah.

Re: Is there something about the slam rules I'm missing?
 

You forgot a few rules, Page 432 of Basic Set. Specifically, The struck object cannot inflict more dice of damage than the striking or falling one. So the most the impala can do is what the cheetah did, 2d.

Also, the cheetah can do an AoA Strong for +2 damage. That gives and average of 9 for the cheetah and 7 for the impala. The cheetah has a higher chance of knocking the impala down.

Re: Is there something about the slam rules I'm missing?
 

The technique I've seen cheetah's use is a Trip. The rest of the cat family mostly Grapples.

Incidentally, the difference in cheetah claws is that they are non-retractable and more similar to canine family claws. Although they are sharp typical cat family claws are also curved and hook-like and should be giving a bonus to grapple.

Re: Is there something about the slam rules I'm missing?
 

It took me an embarrassingly long time to find that rule, especially given that I knew exactly what I was looking for. Under "Head-On", under "Collision angle"? What a weird spot to put it.

Re: Is there something about the slam rules I'm missing?
 

It’s probably my background in Hero System, in which Move Through is a popular attack option, but I’ve always considered the GURPS Slam rules to be deeply broken. There’s just no way to represent the classic bruiser move of putting your shoulder down and smashing into someone (or something), without a lot of fractured shoulders.

And by the way, no cheetah will use any attack mode that inflicts damage on itself. They’re dangerously fragile creatures. Trip seems indeed to be their opening attack of choice, and the rules should probably allow them to execute a full Move and Trip with a fair chance of success.

(Not guaranteed success, of course. Most big cat hunts end in failure and all that.)