The antonyms for the phrase "sprang back" can include "did not move," "remained fixed," "stayed in place," or "held steady." These words all suggest a lack of movement or recoil, which are the opposite actions of springing back. Other antonyms could be "fell forward," "collapsed," "drooped," or "bowed down." These words all suggest a forward or downward movement, which again, is the opposite of springing back. Whatever the antonym, it is clear that the phrase "sprang back" implies a specific type of motion, and its opposite can be found in words that suggest the opposite movement or lack of movement.