Rock Smash is learned by 44 species by level, 397 by machine, 1 by tutor and 5 by egg

Effect, in PokéAPI's words

“Has a chance to lower the target’s Defense by one stage.”

Who learns it

425 species in all, 6 of 20 games shown

Scarlet and Violet: 31 species

Species	Method	Level
Lucario	Level up	1
Trumbeak	Level up	1
Toucannon	Level up	1
Crabominable	Level up	1
Mudbray	Level up	1
Mudsdale	Level up	1
Copperajah	Level up	1
Kubfu	Level up	1
Urshifu	Level up	1
Sneasler	Level up	1
Crabrawler	Level up	5
Passimian	Level up	5
Falinks	Level up	5
Mudkip	Level up	6
Duraludon	Level up	6
Archaludon	Level up	6
Koraidon	Level up	7
Pikipek	Level up	9
Klawf	Level up	9
Cranidos	Level up	10
Rampardos	Level up	10
Cufant	Level up	10
Tinkatink	Level up	14
Tinkatuff	Level up	14
Tinkaton	Level up	14
Riolu	Level up	20
Marshtomp	Egg
Swampert	Egg
Rufflet	Egg
Rookidee	Egg
Corviknight	Egg

Legends Arceus: 14 species

Species	Method	Level
Riolu	Level up	1
Lucario	Level up	1
Heracross	Level up	5
Croagunk	Level up	5
Toxicroak	Level up	5
Machop	Level up	6
Machoke	Level up	6
Machamp	Level up	6
Regigigas	Level up	6
Sneasler	Level up	6
Rhyhorn	Level up	11
Rhydon	Level up	11
Rhyperior	Level up	11
Sneasel	Tutor

Brilliant Diamond and Shining Pearl: 270 species

Species	Method	Level
Marshtomp	Level up, Machine	1
Swampert	Level up, Machine	1
Lucario	Level up, Machine	1
Mudkip	Level up, Machine	6
Riolu	Level up, Machine	20
Bulbasaur	Machine
Ivysaur	Machine
Venusaur	Machine
Charmander	Machine
Charmeleon	Machine
Charizard	Machine
Squirtle	Machine
Wartortle	Machine
Blastoise	Machine
Beedrill	Machine
Rattata	Machine
Raticate	Machine
Pikachu	Machine
Raichu	Machine
Sandshrew	Machine
Sandslash	Machine
Nidoran♀	Machine
Nidorina	Machine
Nidoqueen	Machine
Nidoran♂	Machine
Nidorino	Machine
Nidoking	Machine
Clefairy	Machine
Clefable	Machine
Paras	Machine
Parasect	Machine
Diglett	Machine
Dugtrio	Machine
Psyduck	Machine
Golduck	Machine
Mankey	Machine
Primeape	Machine
Growlithe	Machine
Arcanine	Machine
Poliwhirl	Machine
Poliwrath	Machine
Machop	Machine
Machoke	Machine
Machamp	Machine
Geodude	Machine
Graveler	Machine
Golem	Machine
Slowbro	Machine
Muk	Machine
Gengar	Machine
Onix	Machine
Krabby	Machine
Kingler	Machine
Cubone	Machine
Marowak	Machine
Hitmonlee	Machine
Hitmonchan	Machine
Lickitung	Machine
Rhyhorn	Machine
Rhydon	Machine
Chansey	Machine
Tangela	Machine
Kangaskhan	Machine
Scyther	Machine
Electabuzz	Machine
Magmar	Machine
Pinsir	Machine
Tauros	Machine
Gyarados	Machine
Lapras	Machine
Vaporeon	Machine
Jolteon	Machine
Flareon	Machine
Omanyte	Machine
Omastar	Machine
Kabuto	Machine
Kabutops	Machine
Aerodactyl	Machine
Snorlax	Machine
Articuno	Machine
Zapdos	Machine
Moltres	Machine
Dragonite	Machine
Mewtwo	Machine
Mew	Machine
Bayleef	Machine
Meganium	Machine
Quilava	Machine
Typhlosion	Machine
Croconaw	Machine
Feraligatr	Machine
Furret	Machine
Ledian	Machine
Togepi	Machine
Togetic	Machine
Flaaffy	Machine
Ampharos	Machine
Marill	Machine
Azumarill	Machine
Sudowoodo	Machine
Politoed	Machine
Aipom	Machine
Wooper	Machine
Quagsire	Machine
Slowking	Machine
Girafarig	Machine
Pineco	Machine
Forretress	Machine
Dunsparce	Machine
Gligar	Machine
Steelix	Machine
Snubbull	Machine
Granbull	Machine
Scizor	Machine
Shuckle	Machine
Heracross	Machine
Sneasel	Machine
Teddiursa	Machine
Ursaring	Machine
Slugma	Machine
Magcargo	Machine
Swinub	Machine
Piloswine	Machine
Corsola	Machine
Skarmory	Machine
Houndour	Machine
Houndoom	Machine
Phanpy	Machine
Donphan	Machine
Tyrogue	Machine
Hitmontop	Machine
Elekid	Machine
Magby	Machine
Miltank	Machine
Blissey	Machine
Raikou	Machine
Entei	Machine
Suicune	Machine
Larvitar	Machine
Pupitar	Machine
Tyranitar	Machine
Lugia	Machine
Ho-Oh	Machine
Treecko	Machine
Grovyle	Machine
Sceptile	Machine
Torchic	Machine
Combusken	Machine
Blaziken	Machine
Poochyena	Machine
Mightyena	Machine
Zigzagoon	Machine
Linoone	Machine
Lombre	Machine
Ludicolo	Machine
Seedot	Machine
Nuzleaf	Machine
Shiftry	Machine
Breloom	Machine
Slakoth	Machine
Vigoroth	Machine
Slaking	Machine
Loudred	Machine
Exploud	Machine
Makuhita	Machine
Hariyama	Machine
Nosepass	Machine
Delcatty	Machine
Sableye	Machine
Mawile	Machine
Aron	Machine
Lairon	Machine
Aggron	Machine
Meditite	Machine
Medicham	Machine
Gulpin	Machine
Swalot	Machine
Sharpedo	Machine
Wailmer	Machine
Wailord	Machine
Numel	Machine
Camerupt	Machine
Torkoal	Machine
Spinda	Machine
Trapinch	Machine
Vibrava	Machine
Flygon	Machine
Altaria	Machine
Zangoose	Machine
Seviper	Machine
Whiscash	Machine
Corphish	Machine
Crawdaunt	Machine
Claydol	Machine
Cradily	Machine
Anorith	Machine
Armaldo	Machine
Kecleon	Machine
Dusclops	Machine
Tropius	Machine
Absol	Machine
Spheal	Machine
Sealeo	Machine
Walrein	Machine
Relicanth	Machine
Bagon	Machine
Shelgon	Machine
Salamence	Machine
Metang	Machine
Metagross	Machine
Regirock	Machine
Regice	Machine
Registeel	Machine
Kyogre	Machine
Groudon	Machine
Rayquaza	Machine
Turtwig	Machine
Grotle	Machine
Torterra	Machine
Chimchar	Machine
Monferno	Machine
Infernape	Machine
Prinplup	Machine
Empoleon	Machine
Bidoof	Machine
Bibarel	Machine
Kricketune	Machine
Cranidos	Machine
Rampardos	Machine
Shieldon	Machine
Bastiodon	Machine
Buizel	Machine
Floatzel	Machine
Gastrodon	Machine
Ambipom	Machine
Buneary	Machine
Lopunny	Machine
Stunky	Machine
Skuntank	Machine
Bronzong	Machine
Gible	Machine
Gabite	Machine
Garchomp	Machine
Munchlax	Machine
Hippopotas	Machine
Hippowdon	Machine
Skorupi	Machine
Drapion	Machine
Croagunk	Machine
Toxicroak	Machine
Abomasnow	Machine
Weavile	Machine
Lickilicky	Machine
Rhyperior	Machine
Tangrowth	Machine
Electivire	Machine
Magmortar	Machine
Togekiss	Machine
Leafeon	Machine
Glaceon	Machine
Gliscor	Machine
Mamoswine	Machine
Gallade	Machine
Probopass	Machine
Dusknoir	Machine
Dialga	Machine
Palkia	Machine
Heatran	Machine
Regigigas	Machine
Giratina	Machine

Sword and Shield: 21 species

Species	Method	Level
Marshtomp	Level up	1
Swampert	Level up	1
Lucario	Level up	1
Sawk	Level up	1
Mudbray	Level up	1
Mudsdale	Level up	1
Tapu Bulu	Level up	1
Clobbopus	Level up	1
Grapploct	Level up	1
Copperajah	Level up	1
Kubfu	Level up	1
Urshifu	Level up	1
Golisopod	Level up	4
Passimian	Level up	5
Falinks	Level up	5
Mudkip	Level up	6
Duraludon	Level up	6
Cufant	Level up	10
Sirfetch’d	Level up	15
Riolu	Level up	20
Rookidee	Egg

Ultra Sun and Ultra Moon: 8 species

Species	Method	Level
Sawk	Level up	1
Trumbeak	Level up	1, 9
Toucannon	Level up	1, 9
Crabominable	Level up	1, 5
Golisopod	Level up	1, 7
Crabrawler	Level up	5
Passimian	Level up	8
Pikipek	Level up	9

Sun and Moon: 8 species

Species	Method	Level
Sawk	Level up	1
Trumbeak	Level up	1, 9
Toucannon	Level up	1, 9
Crabominable	Level up	1, 5
Golisopod	Level up	1, 7
Crabrawler	Level up	5
Passimian	Level up	8
Pikipek	Level up	9

Changed over time

One change since Generation II

1. Through Gen IIIPower 2040 from Diamond and Pearl, Generation IV