Pegar en el culo or golpear en el culo are the most accurate translations I can come up with. Pegar is more common in Spain, golpear is more common in much of Latin America; some dialects or specific sentences would skip the “en”.
Other versions are pegar, golpear, apalizar (I’ve never seen it without the leading a-; it would never refer to a consensual act but it can refer to beating someone’s buttocks until the point of causing serious harm), dar una paliza (this is more whole-body), dar cachetes (this can refer to ass or face), dar cachetes en el culo. Dar una palmada en el culo would be “slapping someone’s ass once”; dar palmadas en el culo would be “slapping someone’s ass repeatedly but without force”. Other non-consensual versions include dejarle el culo plano (flattening his ass), dejarle el culo como el de un mono or el de un mandril (to leave his ass looking like a baboon’s), destrozarle el culo (to break up his ass). The places where I say “his” in the translation it’s actually his or hers, the Spanish pronoun isn’t gendered.
Sorry, no identical-meaning one-word translation. They aren’t different languages simply because they have different words, but because they have different concepts.