FUCKING MACHOPS
Machops are my mortal enemy at this point, from Rock Tunnel in Blue and now I meet one at the end of Union Cave in Crystal. My entire party was exhausted, so there was nothing to do but wait for every Mon to be low kicked into oblivion. How do you even kick a plant, a sentient flying rock and a ghost in the nards? I'm assuming that that's what Low Kick does, anyway.
Pokemon Crystal.
Low Kick is basically a sweep to knock them off their feet. Doesn't have a fixed power, its power ramps up against foes that are heavier. Machop's low kick would freaking destroy Geodude (the sentient flying rock, i assume), because super effective + quite heavy. I don't know how your ghost is actually even being hit by it, unless the Machop used Foresight - without using Foresight first, Ghost is immune to Fighting type and Normal type.
I didn't know about the weight bit, but yeah, Ghost-types are supposed to be immune to Fighting-types, without Foresight or Odor Sleuth. I found out about Foresight the hard way myself once, when my Absol got hammered by a Psychic attack. I also discovered that Future Sight(and possibly Doom Desire) also ignores type immunity.
I belive they deal typeless Psychic and typeless Steel respectively - their users get Same Type Attack Bonus from it, but they don't hit as if they were those types.
Funfact: due to the fact that most pokemon get fatter when they evolve, a fully evolved mon with the same Defense as a pre-evolved mon (incredibly unlikely to happen) would probably get hit harder by Low Kick.
As to Low Kick: In RBY, Low Kick had a power of 50, and a 30% flinch chance. Not too bad, but weak.
In GSC, it was same as above, but its hitrate was improved from 90% to 100%.
It was only as of Gen III that its power became variable, where it can range from 20 power (against 0.1 to 9.9kg heavy mons) to 120 power (>200kg), eg Snorlax or Wailord.