始めは処女の如く後は脱兎の如し
はじめはしょじょのごとくのちはだっとのごとし
hide your true strength, and then later swiftly attack the unprepared enemy
脱兎の如く is read as だっとのごとく (datto no gotoku) and means (at) high speed.
だっとのごとく
datto no gotoku
はじめはしょじょのごとくのちはだっとのごとし
hide your true strength, and then later swiftly attack the unprepared enemy