YOU SAID:

I hit him with a pointy rock

INTO JAPANESE

先のとがった岩で彼を襲った

BACK INTO ENGLISH

He hit him with a pointed rock

INTO JAPANESE

彼はとがった岩で彼を殴った

BACK INTO ENGLISH

He hit him with a sharp rock

INTO JAPANESE

彼は鋭い岩で彼を殴った

BACK INTO ENGLISH

He hit him with a sharp rock