The Japanese sentence 空手に先手無し means "There is no first attack (strike) in karate" and reminds us, as Mr. Miyagi would say, "karate is defense only." This is the second rule in Niju Kun, or twenty rules, established by the founder of Shotokan Karate Gichin Funakoshi. For more information see the excellent article Karate ni Sente Nashi: What the Masters had to Sayby Mark J. Tankosich.
空手に先手無し is composed of the kanji空手 (read karate) meaning "Karate", the grammatical element に (read ni) meaning "in", 先手 (read sente) meaning "first move; first strike" and 無し (read nashi) the verb meaning "no; without."