David strapped his sword over the tunic and tried to walk, but he was not accustomed to them. “I cannot walk in these,” David said to Saul. “I am not accustomed to them.” So David took them off.
Jewish Publication Society of America Version (JPS1917) - 1 Samuel 17:39 >And David girded his sword upon his apparel, and he essayed to go, but could not; for he had not tried it. And David said unto Saul: 'I cannot go with these; for I have not tried them.' And David put them off him.