From the inlay (Gremlin Graphics Release):
Three-dimensional simulation of a boxing match. Fight against CIMBEL-LIN, TED MATARE, JANSEN SINO and FIGHTER BULL.
Finish the four rounds, and you will have won the WORLD CHAMPIONSHIP.
On the screen you will see your card, and your opponent's, showing the name, category and weight. There are also two indicators of strength.
To beat your opponent, you must knock him down three times: this will happen when the strength indicator reaches zero.
This game was initially released as "Rocky", but was renamed as "Rocko" in subsequent releases, presumably for copyright reasons.