Pup suddenly terrified to walk up the block

We live on a quiet, dead end street. For us to go on a walk, we must walk the entire block before we can make a turn and start our walks. All of a sudden today, we get 1 house away from the end of the street and my pup went into panic mode. He kept staring statight ahead, and all I could see was the school across the street on the Avenue. No fire, no loud noises, nothing out of the ordinary. We had just taken a walk about 3 hrs ago, and all was fine. He will be 1 yr old tomorrow, and about 85lbs. Hes a gsd/husky/dobie mix. He was so terrified, that even me holding leash with 2 hands and was choking himself. About halfway down the block, I released the leash and told him home. He ran back to our house and yard. I just tried to take him out again, and this time we walked past just 1 house before he again refused to walk, and turned to run home. What could be causing this?